I wrote an image generation program, which took several equations, randomized them, and used them to generate color values based off of a pixel's position in the image. Over 2,000 images were generated by my program, which I left running every night for a couple of weeks, and the images here are all the ones that I found to be the best.
All images are owned by me (and were made by a program that I created) and are under the Creative Commons license. If you intend to use my creation for commercial use, please contact me before doing so.