What is...
PHP is not limited to creating just HTML output. It can also be used to create and manipulate image files in a variety of different image formats, including gif, png, jpg, wbmp, and xpm. Even more convenient, PHP can output image streams directly to a browser via GD. GD is mainly used for creating images at runtime. You can construct graphs, charts, etc using the data available or create custom images based on requirement. For example you can use GD to display the results of a poll. They are quite handy and can provide easy understanding to users.