Description:

gd is the image manipulating library. It was created to allow graphs,
charts and the like to be generated on the fly for use on the World
wide Web, but is useful for any application in which custom images are
useful. It is not a paint program; it is a library. gd library creates
PNG, JPEG and WBMP images. This is a good thing. PNG is a more compact
format, and full compression is available. JPEG works well with
photographic images, and is still more compatible with the major Web
browsers than even PNG is. WBMP is intended for wireless devices (not
regular web browsers).