ImageMagick and GD are 2 of the most frequently used graphic software libraries nowadays. They make the dynamic creation and editing of images and graphs on a website feasible, so they need to be present on a web server if you host your sites on it and you would want to have something different than static images with fixed dimensions. If ImageMagick and GD are installed, you shall be able to edit any image in various ways - create thumbnails, change the colors, flip it, blur it, etcetera. However, these adjustments are feasible if the script application that you employ on your site allows you to do such things. The two libraries can be used with many programming languages - PHP, Python, Perl, and so on., and support over a hundred widely used image formats which you shall be able to work with - PNG, PSD, JPEG, TIFF, GIF and many others.