How to teach image processing and computer graphics to a blind student?
I think you can teach 2D graphics using a tactile approach on a phone or tablet. 

Students are very likely to be used to tracing their fingers over a mobile device (I have watched awesome videos of blind iPhone users in action).

So position and shape change of an object could be detected by them dragging their fingers over to get auditory feedback at the edges. Ideally you want a truly tactile surface but I don't know of any such devices. I have my own reasons for wanting a computer-controlled version of one of these 

For actual image processing maybe map colours to tone, so as they move their finger over an image they hear a tone vary depending on the average pixels underneath. Then, as transforms are applied, the tones would change. You could possibly teach colour theory by varying the mapping to only one channel of RGB.

Update in one of those great examples of synchronicity, a few days after writing the above I was listening to Matthias Tretter of MindNode on a podcast mention how he had been convinced to add accessibility to MindNode, a visual mindmapping product by a blind user. 

His blog posting has videos showing VoiceOver in action. This is a bit tangential to the original answer but a nice anecdote about how preconceptions about the intended purpose of a tool as being visual doesn't rule it out for blind users.