Most www-clients implement several image formats. While format like jpeg or tiff would allow us to efficiently compress photos with lots of colours, graphs that we use in our experiments are often so simple that gif or PNG are sufficient. For several years gd used to be a library that made gif creation quite straightforward. However, gif images use a patented compression algorithm that may or may not need a licence fee. The developers of gd have therefore rewritten the library such that it now produces PNG images.
Updating or animating images is described below.