Image special effects algorithms?

What’s a good source for image processing algorithms to produce special effects (e.g. water droplets, wipes, streaks, tiling, …)?

Thanks for replying. However, I’m looking for algorithms that I would implement using OpenGL/GLSL and DirectX/HLSL.

Are there algorithms that I could readily borrow from GIMP? I’ve used GIMP for quite some time; but, I have not looked at the source.

Ideally, I’d like to find a web site or book describing the algorithms – with examples.

Here’s one such article from GDC 2003.

This paper demonstrates with examples how to use shaders for image effects (e.g. rotations, wipes, ripples) as well as for edge detection (e.g. using Sobel gradient).

Anyone else interested in playing around with a project like this?