ImageMagick is a robust collection of tools and libraries to
      read, write, and manipulate an image  in many image formats
      (over 68 major formats) including popular formats like TIFF,
      JPEG, PNG, PDF,  PhotoCD, and GIF. With ImageMagick you can
      create images dynamically, making it suitable  for Web
      applications. You can also resize, rotate, sharpen, color
      reduce, or add  special effects to an image and save your
      completed work in the same or differing image format.
     
Note: 
       The above text is from the ImageMagick Website 
       (http://www.imagemagick.org/),
       therefore not everything does apply to this extension at
       the moment, but it will some time in the  future.
       Hopefully. And the link above is also a great source, if
       you don't understand everything here.
      
      imagick went through a major upgrade with version 0.9 and is not backwards 
      compatible to older versions. You should look at the examples, which come 
      with the package, for some documentation about the new API.