Ask Slashdot: How To Catch Photoshop Plagiarism? 284
First time accepted submitter jemenake writes "A friend of mine teaches electronic media (Photoshop, Premiere, etc.) at a local high-school. Right now, they're doing Photoshop, and each chapter in the book starts with an 'end result' file which shows what they're going to construct in that chapter, and then, given the basic graphical assets (background textures, photos, etc.), the students need to duplicate the same look in the final-result file. The problem, of course, is that some students just grab the final-result file and rename it and turn it in. Some are a little less brazen and they rename a few layers, maybe alter the colors on a few images, etc. So, it becomes time-consuming for her to open each file alongside the final-result file to see if it's 'too perfect.'" How to look for images closer than they should be to the original? Read on for more details.
jemenake continues: "When I first discovered that she was doing this, my first reaction was that there's got to be some automated way of catching the cheaters. Of course, my first idea of just doing MD5 hashes of each file won't work, since most kids alter the file a little bit.A second idea I had was to alter the final-result file in a way that isn't obvious, like removing someone's shoelace, mis-spelling a word in the background, or removing/adding some dust-specks. (I know map publishers and music transcribers use this trick to catch copiers). But this still requires that she look for the alteration in each file. I'd think that Photoshop, after all these years, would have some kind of scripting language which also supports some digital watermarking, but I've just never dabbled in that realm.
And, of course, I guess another solution would be for her to not provide the end-result file in Photoshop format, but to export it as a flat image. But I'm still intrigued by the notion of being able to "fuzzily" compare two photoshop files or images to find the ones which are too similar in certain aspects (color histograms, where the edges are, level of noise, whatever).
Anybody else have any clever ideas for this?"
Invent your own exercises (Score:5, Insightful)
That's what a teacher is supposed to do anyway.
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Or just provide a similar base image for all to use. They can still use the textures and extras.
She could try... (Score:5, Informative)
Perceptual Image Diff [sourceforge.net] and Find Image Dupes [freecode.com] might be helpful. If she runs finddupes with a threshhold of .99 or so, then it is likely just trigger on nearly exact copies. At least, it should narrow down the ones she has to inspect in more detail. On the other hand, pdiff will detect exact or nearly exact copies by specifying how many pixels are allowed to differ (so it can be fooled by addition of random noise). While pdiff is available for Windows as well as Linux, it seems that finddupes is Linux only.
Re:Difference layer effect is even easier, (Score:4, Funny)
"It's fun to do this with NASA photos of the moon, some of them have lens flares added from photoshop. :) (you can recreate some the lensflares pixel perfect...)"
Not at all, those are the files photoshop's lens flare is based on.
Re:Invent your own exercises (Score:5, Insightful)
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Throw out the cookie cutter (Score:5, Interesting)
Let them use their own base images! And then let them do something creative with them!
One of the least interesting and least creative classes I took in art school was one that was about producing photorealistic oil paintings based on photographs. The class was 99% about mechanical technique, and to hell with creativity... which seems to be the theme of the class being taught here. So be it. But at least the instructor let us pick our own photographs to replicate! So we'd have an interest in what we were doing. And even if he had never checked on our progress along he way (like would happen in any worthwhile "learn how to ____" class), he would know whether we had done the work, because each of our paintings was a) unique, and b) matched the photograph we'd had approved at the start of the assignment. Plagiarism wasn't even a question, and not just because we were working in traditional physical media.
All of these suggestions for how to identify plagiarism through technological measures are missing the point. The problem isn't "how to catch a cheat", but "how to give students an assignment that they will have a reason to bother doing in the first place".
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This is a great idea, unfortunately it falls flat in the face of reality. I used to teach computers, and spent a lot of time coming up with (what I thought was) neat assignments. Students would photoshop themselves into historical photos. They would creat
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Or view exercises for what they are... exercises. The test/final project is what it is. Maybe your students don't need the exercises because they already have a strong grasp of the task.
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Newsflash: Students usually cheat because they DON'T have a strong grasp of the task.
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Newsflash: Students usually cheat because they DON'T have a strong grasp of the task.
Not necessarily. There are many reasons that people cheat:
1) They are lazy
2) They "don't have the time"
3) They think they're getting away with something
In these cases they use "I don't know how to do it" as the excuse to just cheat, rather than expend the effort required to ask for clarification or practice further until they do grasp the task/concept that they are performing.
For some reason in college (at least my college), people cheating is totally normal and students talk about it like it's no big deal.
Re:Invent your own exercises (Score:5, Insightful)
It's of course easy to invent your own exercises, but even better would be to have the students to use pictures they have taken themselves to be used in the exercise. And almost everyone has a mobile phone with a camera these days so that would be a minor problem. Or provide a collection of pictures that can be used in the exercise and let them play around.
Just state the basic points, then let each student do what they can and let them rate each others results. Don't force the students to use the same template, let them have their artistic freedom.
And isn't the whole point behind the exercise to learn how to use Photoshop and other tools - not to try to mimic a creation?
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OMG, are you really saying that both the teacher and the students are supposed to be creative and move beyond the exercise description in order to learn more and even have fun while doing it?
You, sir, disgust me. I am shocked, shocked I tell you!
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(I am a music teacher, but want to add to the discussion from an arts perspective)
Not every person in every discipline should re-invent the wheel at all times. Though as an expert (assumably) you should be coming up with your own material, there are other instances where there are resources which are as good as anything you'd put together on your own. Including assignments.
In this case, however, I think there's an important consideration. Even if the primary focus is to learn Photoshop, this is an arts c
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Yes, cause what I want my kids teacher doing is repeating the same damn work that's been done countless times over by other educators all over the world.
It's a little like someone asking how to sort an array in Java and being told "write your own sort algorithm, that's what a programmer is supposed to do anyway".
Rather than having every single teacher re-invent all of the same assignments, I'd rather they spend some time studying methods for teaching to different learning styles. Or developing on standard
Re:Invent your own exercises (Score:4, Insightful)
There are some good problems that have been asked over and over again because they teach good lessons. My data structures professor started one of our assignments off with the following quote "More time has been spent on undergraduates recreating the Ackerman function than any other problem in computer science, and you all will be no different"
Sure there are other problems that have double recursion but why try to find something new and different when a good problem already exists? Plus there is something unifying about it. If I meet someone who graduated years before me or years after and they also had to do the Ackerman function in some language maybe the same one I used it kind of give you something in common. I like that; a common thread the ties us all together.
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I'll agree that it's a poor analogy. But what I'm saying is more equivalent to asking the teacher to invent a new medium, like the soft part of feathers to paint on ceramic or something.
Still, I think that telling teachers that they have to invent their own exercises is a poor choice, since it's hard to make good exercises. And it's really easy to make bad, poorly-defined ones.
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I believe that what you're complaining about, is exactly what separates excellent teachers from mediocrities who are looking for tenure. A teacher who is incapable of making up his/her own exercises probably doesn't understand the content that they are teaching well enough to be teaching!
To be fair, it may take a lot of time to create an exercise. So - a good, motivated teacher does two or three such exercises this year, and saves them. Next year, two or three more - and saves those for future use as wel
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I believe that what you're complaining about, is exactly what separates excellent teachers from mediocrities who are looking for tenure. A teacher who is incapable of making up his/her own exercises probably doesn't understand the content that they are teaching well enough to be teaching!
To be fair, it may take a lot of time to create an exercise. So - a good, motivated teacher does two or three such exercises this year, and saves them. Next year, two or three more - and saves those for future use as well. In five years, Teacher has all the textbook examples, plus a library of his own to draw on. Teach isn't restricted to the material that the students find in their textbooks, he has tools at his disposal to help him find the cheats.
The textbooks and workbooks are only aids for a good teacher, not the crutches that most mediocre teachers rely on.
Nice theory. If it's true, so what? The reality of the situation is that we also rely on mediocre teachers, because there simply aren't enough excellent ones to go round.
But is it true? Well, as a teacher, I'm predisposed to say "no", amn't I? So it'll be no surprise that I say "no", then. First up, you haven't even addressed the core problem here -- even if the teacher makes his own tasks, he's still reusing them, and they're still going to be the same for all his students.
But more than that, there ar
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Sure. And it's hard to build a well constructed chest while being really easy to build a shoddy one. Yet we still expect people who we pay to build chests to build them well. I'm not sure why that doesn't apply to people whose job is to teach being expected to perform the various parts of teaching well.
But it seems like a trivial situtation to me - then again I'm don't do photoshop or art so maybe there's something tricky. Just give the students the flattened compressed to crap jpeg export of the final imag
Re:Invent your own exercises (Score:5, Insightful)
Or require students to also hand in the intermediate steps for the homework just like old school math.
At the start of the course have a discussion about ethics and expectations. Have a class discussion of the purpose of the exercises. Have the class participate in designing the evaluation scheme (percentages for HW, tests, etc.) Get them to buy into the course so they view it as something they are participating in because they see value in their participation. Have them turn in some intermediate steps, and maybe some commentary on things they found challenging or interesting about the activities.
Record transgressors and use the policies of your institution to at the very least get it into their institutional record if they commit any accredited dishonesty so that if they have a pattern of that type of behaviour they can be tracked.
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Record transgressors and use the policies of your institution to at the very least get it into their institutional record if they commit any accredited dishonesty so that if they have a pattern of that type of behaviour they can be tracked.
I meant to say "academic dishonesty" rather than "accredited dishonesty", though if you can get their dishonesty "accredited", more power to you.
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We are talking about an image which they said had layers.
Give them the final image as a flat raster image file, say JPEG or PNG. Since they must be turning their work in as a PSD (Photoshop format) or similar file if it has layers and all that, no problem at all. If for some reason you need to include a sample PSD file so they can see what different layers do, make it of a completely different image.
Don't forget, you may have someone in the class who really is willing (sometimes) to do 3 times as much work
She should know this if she's teaching photoshop (Score:5, Interesting)
Paste images into the source image as new layers, adjust layer mode to "difference" and look for the similarities. Done.
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Depending on what the exercises are, they might not leave much room for slight differences. "Construct a rounded rect button with 12 px radius corners with a vertical gradient from #RRGGBB to #RRGGBB and a 15% drop-shadow with radius of 7px offset by 14px at 120."
A better solution is to digitally watermark the solution files, or if the students have access to the solution files independently (i.e. they came with the book on a CD), watermark the source files and require students to start with those rather t
Final result should just be a flattened image? (Score:4, Insightful)
Why not just flatten the final result into a simple image? The students can still see what the end result is supposed to look like, but they obviously can't just hand in that file.
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Why not just flatten the final result into a simple image?
You know how I know you didn't even bother to read the entire question...?
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Just because it was posted as part of the question doesn't mean it's not a good answer. It certainly seems to be the easiest, and most effective way to detect the problem quoted.
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Just because the writer dismissed the perfect answer doesn't mean you can't ask them why they don't use that obvious simple solution.
MOD PARENT UP! - Re:Final result should just be (Score:5, Insightful)
Why not just flatten the final result into a simple image? The students can still see what the end result is supposed to look like, but they obviously can't just hand in that file.
Offer flat JPG in medium quality as an "end result". Maybe even include a digital metadata watermark?
Require high quality JPEG and PSD for assignment. First check for metadata watermark, then compare quality of JPEG. If it looks too close then open up the PSD and check the layers.
Re:Final result should just be ascii (Score:2)
Don't Give Them The File? (Score:2, Insightful)
How about simply not giving them the final file? Why not a printed copy?
If they must have an electronic version of the picture give them a low res thumbnail version.
Project the image on a screen and tell them to draw that.
Your problem is that you are over thinking the tech angle when low tech methods will be super effective.
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simple solution (Score:5, Informative)
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Or if they want to distribute the final file for reference purposes, simply distribute it at lower resolution than what you require the students to do. Problem solved.
MadCow.
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The stated problem was how to stop people from copying the example file and handing it in as their own work. The suggested solution solves that problem perfectly. (unless you think it's easy to de-watermark a png and then separate it out in to believable layers in a psd file? (or at least easier than just doing the assignment))
How to stop students from cheating by copying each other is a completely different problem, and luckily, not what the submitter asked. (because there really isn't a "good" way in that
Re:simple solution (Score:4, Interesting)
This should work and would be trivial to do.
If you want to spend more time on it, make sure that the student's copy of Photoshop is set to record history in the metadata.
Then you can go through and look at every step they made. I do this on some images so I can figure out what the hell I did to get that effect three years later. It takes up little space - it's just text.
But a more boring way to spend a day would be hard to create.
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distribute the final file as a watermarked png only. Require assignments to be turned in a multi layered psd files. Problem solved.
What is to stop the kids doing that as a final step, and giving their assignments to others, who also add the watermark as a final step? You need to think before you suggest something.
Sounds like you need to read before insulting. The parent's solution works perfectly for the question asked.
Don't give out the answers (Score:2)
Provide the book resources as a tutorial but get the students to do something different for the actual assignment. It could be as simple as swapping a few textures or effects. A blur on a cat will look very different to a blur on a dog even though the technique is the same.
Instead (Score:4, Interesting)
She could also not show the students a picture of the final project. She could just give them a list like:
1. Remove one set of shoelaces.
2. Add a bird in the sky
3. Add a portrait of Spock in the background.
etc.
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More like:
1. Remove the stretch marks
2. Make the boobs bigger
3. Get rid of that wart thing with the hair growing out of it.
etc.
Re:Instead (Score:5, Funny)
Re:Instead (Score:5, Funny)
It certainly jazzed up our family reunion photo!
suggestion (Score:2)
supply the desired end result to the students in hardcopy, ask for their results in electronic format. Oh, and hide the SCANNERS!
FindImageDupes (Score:5, Informative)
From the manpage:
findimagedupes [jhnc.org] compares a list of files for visual similarity.
To calculate an image fingerprint:
1) Read image.
2) Resample to 160x160 to standardize size.
3) Grayscale by reducing saturation.
4) Blur a lot to get rid of noise.
5) Normalize to spread out intensity as much as possible.
6) Equalize to make image as contrasty as possible.
7) Resample again down to 16x16.
8) Reduce to 1bpp.
9) The fingerprint is this raw image data.
To compare two images for similarity:
1) Take fingerprint pairs and xor them.
2) Compute the percentage of 1 bits in the result.
3) If percentage exceeds threshold, declare files to be similar.
Of course, you shouldn't take its suggestions at face value every time, but it should help narrow your search for cheats.
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To expand on that, you could also use ssdeep to calculate a fuzzy hash of each picture. [sourceforge.net]
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Given that the students are supposed to reproduce the images, I guess they will get a high visual similarity, unless they failed.
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How on earth is smart AC modded 1, and the OP is +5 Informative? Attention: mod points needed.
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Wouldn't re-sizing the image to 160x160 basically wipe out so much of the detail as to lose a lot of precision?
I should think most things people doing in Photoshop on a decent megapixel image would essentially become noise at that resolution.
My 12 megapixel camera takes images at 4000x3000 ... 160x160 is trivial in comparison.
OP already has the answer? (Score:3)
You already mention the solution, why be silly about it? Just watermark the images and hand them out as jpegs, not photoshop files.
You could obviously watermark each individual layer if you wanted to give the photoshop files, but why would you want to do that?
Simple Solution (Score:4, Insightful)
Give a token homework grade (like ~ 10%) for participating and make everything in the final grade else be based on original projects and tests. Make the students use given files.
Then, if they cheat, they only cheat themselves.
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Came to say this. Don't even collect homework/classwork. Give them 10% for attendance. Don't take attendance. Just give them 10%
If they can't do it at the end, they will fail. If they didn't ask for help, tough. Treat them like adults. They will ether rise to it or learn what doesn't work.
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"If they can't do it at the end, they will fail. If they didn't ask for help, tough. Treat them like adults. They will ether rise to it or learn what doesn't work."
While that is a fair approach, I've found that I get much higher success rates in the end if I have some kind of feedback during the period they are working. If they don't *know* they're way off track, or don't *know* they aren't putting in enough effort, then, sure, they'll fail at the end like they should, but there will be some missed opportu
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I never struggled with a subject and didn't know it at the time. Not to say that a word from the teacher can't help the student rise to a challenge.
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In creative pursuits like Photoshop, you have subjective quality concerns. If you copy and paste a head from one picture onto a body in another and there's huge jaggies around the head, and no color matching, you might still be dumb enough to not realize you're off track. Or, get the edges perfect and still don't realize that it's not color matched, or that the shadow directions don't match.
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I'd guess the students previous teachers have failed to teach them 'what doesn't work'. A teachers job is to teach students how to learn without a teacher. Any facts or skills they get along the way are just bonus's.
My sympathies. Perhaps high stakes chapter tests. I'd be damned if I would grade homework for fucking college students.
Ummmmm (Score:5, Informative)
ComparePSD compares two Adobe Photoshop PSD files for you and highlights the differences. Layer by layer. Effect by effect. Simple. And did we mention that ComparePSD is absolutely free?
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There are other algorithms that work on the final result to tell you how much of the photo was changed.
Since she has the originals, something like this would work: Auto compare every final picture with its original and produce a number, percent changed. Then use ComparePSD to compare the submission that are the same % changed.
The problem is that if she is too specific in her instructions for the assignment, then everyone in the class that tries will have the
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Of course it's time consuming. Isn't that partially the point?
I understand that the question as is left at the end of the submission is just a case of curiosity and there's plenty of good answers to the question here.
But the problem being described is entirely separate from that question - and the problem seems to be that there's a teacher who sets time-consuming tasks but does not want to do time-consuming review.
I find it rather similar to math teachers.
Some math teachers will give you a test and they ju
history (Score:2)
A quick review of the history should tell you a lot. If it's exactly duplicated with a few tweaks at the end, it's a dead giveaway.
Re:history (Score:5, Informative)
Yep. PS does include a history function that can be written to the metadata. Bonus points for pulling out the metadata stream, running some regex on it and deciding if it was legit.
Extra bonus points for not including the history in the image given to the students. And requiring it for a grade.
Crop the example result files (Score:2)
Students must turn in the full image. Much simpler than watermarking.
be smarter (Score:2)
for one assignment students turn in their own pictures with themselves in it near some assigned object. Later, another assignment has them work with their picture toward some given result on the object, with them still in the picture.
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for one assignment students turn in their own pictures with themselves in it near some assigned object. Later, another assignment has them work with their picture toward some given result on the object, with them still in the picture.
It's a good chance that the more photogenic students will get the highest grades. There are several studies about grad student grant proposals that back this up.
Criteria (Score:2)
> So, it becomes time-consuming for her to open each file alongside the final-result file to see if it's 'too perfect.'"
How is it that she's grading these? One would assume the grade depends on similarity to the target image or the layers embedded in the file [1] which should be dependent on comparing the student file against the master.
Or is it yet another "Best try" scheme? "You tried, Timmy, so I give you an 'A'".
[1] Does Photoshop embed the history inside the file? It's been awhile since I've work
Flatten The Example. (Score:2)
And, of course, I guess another solution would be for her to not provide the end-result file in Photoshop format, but to export it as a flat image. But I'm still intrigued by the notion of being able to "fuzzily" compare two photoshop files or images to find the ones which are too similar in certain aspects (color histograms, where the edges are, level of noise, whatever).
If you provide the kids with the end result, and they need to turn in an end result for grading, you're fighting a losing battle. I could personally get around everything you did to try to protect your "example" PSD, and I'm relatively certain that I could have done so at the age of your students. Just give them the flattened image, it's enough for them to see what it should look like.
You should still, of course, use one of the methods mentioned in sibling posts to compare submissions for too much similar
Do what I do for my textures (Score:3)
Do what I do for my textures, and embed a "watermark" of your signature or something similar deep into the final image where it can't / won't be seen by anybody who doesn't know where or what to look for, in multiple places where the pixels are conducive to such masquerading. It's almost a form of steganography, where the message to be sent is a verification of the authors' identity and claims of original work.
I do mine in such a way that even if I leave one such image that can be readily seen, there are at least a half dozen more than cannot be found without a side-by-side comparison of source and production images with and without the "watermarks" (impossible without someone getting hold of my .PSD's). Keep the true "source" .psd for yourself, create another for disbursing to students that contains several "watermarks" with an extreme level of transparency well-blended into many or all of the layers so they'll have an example .psd to "reverse engineer", and then separately give them the actual un-watermarked original source images, which they should then be expected to chuse to assemble the final image themselves. You might even put an entirely separate watermark into the source images, so you can check to see which watermarks the submitted image has, as opposed to checking only for the source mark.
If they put in enough time and effort to actually successfully circumvent this technique by finding and either eliminating or duplicating all the various marks, then they've probably got the requisite skills to pass the original challenge... at least if you do it the way I do.
My "signature" is in at least 3 places in this image [photobucket.com], buried deep in different layers with heavy transparency masks, and it would have to be altered drastically to be guaranteed to remove all traces of it.
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Difference Filter + Histogram for Numeric Measure (Score:2)
You can use a difference filter, which will produce a ratio of dark/light based on the amount of difference, and then a histogram to get a more quantitative view of how much of the image is different, rather than analyzing with your eyes. You could do this on both flattened composite comparison, as well as layer by layer(maybe trying all combinations of layers and picking out the X number that are closest, where X is the number of layers in the final image). I'm not sure what the capabilities of Photoshop
Introduction to Time Lapse (Score:4, Interesting)
It's probably annoying for all involved, but just like the "show your work" in math classes, you can request a "show your work" equivalent via screen-cast. And the students will learn a bit about screen-casting.
Alternatively, request a picture of each step.
Something about Forest and Trees (Score:2)
A second idea I had was to alter the final-result file in a way that isn't obvious, like removing someone's shoelace, mis-spelling a word in the background, or removing/adding some dust-specks. (I know map publishers and music transcribers use this trick to catch copiers). But this still requires that she look for the alteration in each file.
Ummm, maybe I'm missing something here? She should be looking at the file, right? What's the harm in checking one little thing as she's looking at it? I mean, how else is she going to be sure they actually did it properly without checking it anyway? Zero solutions should allow her to skip checking the homework entirely, if it does, its kind of missing the point.
While the flat no-layered file is the obvious solution, it will have an unintended side effect of not acting as a fall-back guide for students w
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Wait, wait, wait. You mean you want the teacher to grade he assignment too? Who do you think they are, miracle workers?!
Duplicate Photo Finder (Score:2)
I teach online. (Score:2)
We require that they take screenshots while working, and they submit the screenshots as a multi-page PDF.
Also, as everyone else is saying, don't distribute the final file. If the files come from a 3rd party (like lynda.com) then add a few more steps onto the tutorial.
Change the assignment (Score:4, Insightful)
The teacher needs to stop trying to figure out ways to catch people cheating on an exercise designed for cheating and start teaching the damn course. Teaching doesn't just mean lecturing and assigning exercises out of some book, it means developing exercises, homework problems, and exams from scratch as well.
This is photoshop 101 kind of stuff... (Score:2)
If she does not want them to use her assets, Embed each asset with a visible watermark. Come on, is this photoshop teacher a newbie?
"Too perfect"? (Score:2)
How can the product be "too perfect" when the products should be identical? Ok, date stamps and maybe embeded path names will be different, but the image itself, starting from the same sources, doing the same things, should be the same.
Maybe the problem is that t
Why does this sound like a stock image supplier? (Score:5, Interesting)
Why does this sound like a stock image supplier trying to find machine-modified infringing images using a web crawler so that they can bludgeon the people publishing the modified images, who have not paid a license fee, with a copyright infringement lawsuit?
I'm just saying, a good answer to the OP's question is going to mean the ability to use the answer in this fashion.
My solution (Score:2)
Simple answer: Test them (Score:2)
Honestly, the best way to catch the cheaters is to test them. If they aren't doing the work, they aren't learning the steps. So hold a few tests throughout the term and make the tests worth more than the assignments. Show them, not give them but show them on an overhead projector or using a large photo, the end result that is required. They have 30 minutes to produce it.
Wrong lesson anyway (Score:2)
Rather than having them copy the output. Give them each a different set of art assets, and have them each turn out an original work using the lessons -taught and shown- by the example. Then there's no copying, and they might actually learn something.
Submit screencast + final image (Score:2)
This is basically the digital equivalent of "show your work" on a math test. If you want to see how well the students are grasping certain concepts, tell them to include an audio track in which they describe what they're doing and *why* -- e.g. "lightening this layer now because I did *blah blah* and messed it up previously".
Anyone who is good enough to fake the screencast convincingly probably doesn't need this class. And if you're really concerned about people using a ringer to do their work, have an in-p
Don't give them a PSD of the final result. (Score:3)
Duh. Flatten the final picture. You will still have outliers who can make it look convincingly different enough but it won't be as easy as giving them access to each individual layer for them to fudge up.
Also consider embedding tiny watermarks in the image. Little sets of pixels at specific coordinates. Not specifically exact colors but something you would be able to identify on close inspection. Something like a small 6x6 checkerboard grid of alternating light colored pixels in a light area of the document that wouldn't be easily seen by your students but you could zero in on and verify.
Don't bother/honor system (Score:3)
Don't give them the answer (Score:3)
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Not a bad idea. That would probably catch most of them...
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One poster suggested that each student gets a slightly different original file. Something like different house numbers, but in the same font and color. If two students submit the same house number, you know they copied.
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Steganography?
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Also make it clear early-on that this class is designed to teach them a useful, marketable skill and that if they cheat, they won't have learned the skill and if enough of them cheat and don't get caught, YOU won't know to slow down the pace of instruction. As a result, the whole class may "pass" knowing a lot less than they would if nobody cheated.
Some artists/journalists would argue that *any* use of photoshop is cheating. Albeit, it's not copying, but you are bending reality. (Not that photo manipulation is new to photoshop. Trick photography started just a few years after photograpy itself was invented, and even realist painters didn't paint the "real", reality)
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I wish someone had taught us Photoshop or any other useful 21th century stuff in high-school.
So do the rest of us who have to look at the awful Photoshop [psdisasters.com] stuff that floats around the Internet these days.
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Let them grade each other. Of course you will need to anonymize the submissions so that only the creator knows that the picture is his.
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I agree - a blank slate is the best, in the real world you have to be creative.
Just state that they should have a picture with an animal, a beverage and a well-known landmark and that some types of transitions and effects are expected. But then also state that they aren't limited to that but can do something completely different as long as they have a certain number of effects in the image.
And to make sure that they don't copy an existing image they should provide the source images used too.
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binary compare? Open image, save as JPG. Completely different contents to the file. Unless the world switches to lossless images all around and bandwidth makes some pretty big leaps.
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