ImageMagick and GD are two of the most widely used graphic software libraries available. They make the dynamic creation and editing of images and graphs on a website doable, so they must be present on a server if you host your internet sites on it and you would like to have something different than static images with fixed dimensions. If ImageMagick and GD are set up, you shall be able to edit any image in many ways - generate thumbnails, change the colors, flip it, blur it, etcetera. However, these modifications are possible if the script application that you use on your internet site permits you to do such things. The 2 libraries can be used with a lot of website development languages - PHP, Python, Perl, and so on., and support more than a hundred frequently used image formats that you'll be able to work with - PNG, PSD, JPEG, TIFF, GIF and many others.