Visualizing difference image without exposing the solution itself

I want to add some helpful feedback to student submission in Cody Coursework, for example when filtering an image. This way I want to show a difference image (which is a difference between the student submission and true image). However, I do not want to directly expose the true image, because then the students can just upload that data.

When I try to do something like this using hidden tests, no graphics can be visible to students. When I then try to do this using visible tests, it is not possible to hide the solution itself from the student (see screenshot below for pixelized region for an example). I would not consider p-files as they are not safe to give to the student - will be cracked and the homework will be compromised.

Best regards,

D. Bobkov

Answer 1

[Walter Roberson]

If you show an accurate visual difference, then if the student submits an all-zero image, the visual difference would be the same as the correct image (or would be its negative).

You could watermark the difference image (perhaps visually so), or you could show only part of it. Or perhaps you could present a downscaled version of it.

Is the question about how to have exposed code which cannot be extracted to give the answer?

[Dmytro Bobkov]

Of course we do not plan to show the full-size difference image, but rather a small version. Yes, the question is about how to hide the code that produced that true image.