ImageMagick and GD are 2 of the most widely used graphic software libraries out there. They make the dynamic creation and editing of images and graphs on a website feasible, so they should be present on a web server if you host your sites on it and you prefer to have something different from static images with fixed dimensions. If ImageMagick and GD are present, you shall be able to edit any image in many ways - generate thumbnails, change the colors, flip it, blur it, and so forth. Of course, these modifications are doable if the script application that you use on your website permits you to do such things. The two libraries can easily be used with a lot of web development languages - PHP, Python, Perl, and so forth., and support more than 100 popular image formats that you shall be able to work with - PNG, PSD, JPEG, TIFF, GIF and others.