[SCRIPT3R]

Originally Posted by vBulletin

vBulletin provides two options for manipulating attachment thumbnails, custom avatars, and profile pictures.

The first is GD, which is bundled with PHP 4.3.0 and later and often available with earlier releases. The GD v2+ library is preferable to the v1+ library so always choose v2 if you're given the opportunity by your host. GD supports the following file types: GIF, JPEG, and PNG.

The second supported library is ImageMagick v6 by ImageMagick Studio LLC. ImageMagick is an executable binary that must be installed at the server level to be called by PHP. Only the identify and convert binaries from ImageMagick are required by vBulletin. ImageMagick supports the following file types: GIF, JPEG, PNG, BMP, TIFF, and PSD. ImageMagick also has better support for handling animated GIF.

thought better explained via vB.