Ask HN: How to programatically photo-manipulate two images?

Basically, I'd like to create an online tool with which people can upload an image and somehow automatically superimpose it and then shear/stretch/scale it to fit specified areas on top of that image. I'd know how to do it manually with GIMP, but I was wondering if there's a way to do with programatically, provided that I can hard-code fixed sizes and dimensions for everything.<p>Thanks<p>TLDR:Is there a way to programatically photoshop something?