GD is an open source code library for the dynamic creation of images
by programmers. GD is written in C, and "wrappers" are available
for Perl, PHP and other languages. GD creates PNG, JPEG and GIF
images, among other formats. GD is commonly used to generate charts,
graphics, thumbnails, and most anything else, on the fly. While not
restricted to use on the web, the most common applications of GD
involve web site development.