What is the correct way of saying the following?
I want to evaluate your opinion and comprehension of/about this image?
You'd want to use of here.
About would pair nicely with opinion if it were on its own in the sentence; however, of pairs just as well with it, and must go with comprehension.
I feel that the two concepts - comprehension and opinion, are too different to be combined together in the same expression. To me, comprehension is objective and opinion is subjective. Are you interested in the kind of comprehension that is quantifiable, e.g. is the person able to find 10 differences or find hidden objects in the image? Or are you soliciting their subjective opinion on art?
If the latter, I would rephrase the question to something like this: I would like to know how you interpret this image and your opinion of it.