what is the best way to place a picture onto a surface? Let me explain my problem.

I want to put a picture of a hippocampus (slice of brain) onto a model of a hippocampus that I build. I first made the hippocampus shape out of NURBs (see picture below).

I wanted to put thisl picture just on the top surface of the model.

1) how do I prevent it from wrapping all the way around the whole surface?

2) how do I map a "non -square" image onto a surface. Image is oval without any background in Photoshop, but white backgorund shows up when i import it (like the photo below)


Thanx for any help......here's a picture of what I am trying to make..minus the white outer section