Image Shuffling

Ok. I need help or just a tip so let's see how fast can 4channers solve it.

I have one big image which is a grid of symbols. Each symbol is exactly 20x20px. They are ordered and I need to shuffle them randomly.

I'm not gonna do that manualy because the image is really big and I am fucking lazy. There must be some app or plugin, but I don't know how to ask Mr.Google. Or I should write a script but I am too lazy to rediscover the America.

Any suggestions?

Instead of one big image, you want lots of 20x20 images that you can programmatically place in random locations.

If you're not doing this in a program, then you're a moron for asking on /prog/.