Well there are at least 2 ways to proceed. You could certainly do it with Obj-C, and that's how I would do it but only because that's what I am most familiar with. You could also attempt to do it with Quartz Composer. QC is a really powerful tool that lets you create graphical compositions. It's hard to describe in a few sentences but think about a toolbox where you can drag out various tools (patches) and connect the patches together like a pipeline. If you get into it, you might find that it's not practical with QC but keep in mind that I don't fancy myself a QC expert. I know just enough to do the basic stuff.
That being said, Obj-C/Cocoa is a really great programming language/environment. If you're strong with Java, I imagine you'd pick up the basics pretty quickly. From there, I could send you a Hello World CamTwist plugin and help you get it going.
Do you know C?