How can I scroll a picture and know where I clicked

[Moose On The Loose]

I can view a large picture with something like viewnior. So far so good but now when the user sees the puppy hidden in the picture, I want them to be able to click on it to point it out. If the picture didn't scroll, I could work it out by picking of the mouse click location. I, however need the picture to be able to be scrolled.

Any suggestions?

I am up for a little C program hacking if needed but if someone has already done this, repeating the effort would not be the best use of my time.