any way to use a custom image renderer?

I have a requirement for a ecommerce solution whereby a user selects several attributes of a product

for example:

left piece
middle piece
right piece

think for instance of a custom bookshelf creator, where we have varying types of cabinets and bookshelves, some with doors, different heights etc.

and we then, as the 3 pieces are selected, we need to merge the 3 sub-images on the fly into one combined image so they user can see the end result.

Has anyone done something like this before, and are there any example sites that do it or modules that already exist?

Barring that, I was imagining that there would be a bit of "image updating" code that I could override, and add my own custom code to grab each image and merge them myself?

I look forward to hearing your thoughts.