Thank you Abrita, you're very kind. Since Wolfram U's policy is to pass people with a 60-70% score and not display the final score, I have found it very easy to pass most of the courses I have taken even with some of my good answers being marked incorrect. I think that's actually a great policy because allows me to focus on understanding rather than revert to a student psychology of getting the best grade. :)

Dear Abrita,

I have the same issues with some of my exercises solutions in some sections. The autograder marks mine as incorrect, and I am sure they are correct. For instance, when I substract the image solution expected to mine, I get zeros (a black image, no negative pixel values), so the solution is right, though is graded as incorrect.

Anyway, I can read that sometimes the autograder cannot check all possible solutions. If the autograder is still evaluating my solutions incorrectly, can I submit all my exercises by email?

I am almost finished the course, and I can say that is very satisfying to pass it. I found it very instructive and a good introduction to Image processing. I have remembered some things what I learnt some years ago, and learned some news.

I recommend it to those interested in Image Processing using Mathematica.

I was able to get things to work with:

FindFaces[ResourceData["Exercise Images for Introduction to Image Processing MOOC", "Kids"], "Image"]

and

Classify["FacialGender"][FindFaces[ResourceData["Exercise Images for Introduction to Image Processing MOOC", "Kids"], "Image"]]

This was one of the few times WolframU was very particular on how things were done.