The Image_Transform package is useless without a driver that encapsulates some graphic libraries' methods. As of April 2008, the package has the following drivers you can install and use:
Image_Transform_Driver_GD - uses methods of the GD 2 extension
Image_Transform_Driver_Imagick2 - for imagick PECL extension version < 2.0
Image_Transform_Driver_Imagick3 - for imagick PECL extension version >= 2.0
Image_Transform_Driver_Imlib - uses PHP imlib extension
Image_Transform_Driver_IM - Imagick binary executables (if you don't have the extension)
Image_Transform_Driver_NetPBM - uses the binary executable pnmscale of the NetPBM software package.