ImageMagick and GD are software libraries that should be present on a web server for images to show up on a specific site. They permit you to perform a variety of tasks with the images - create, flip, resize, change colors, and so forth. These things can certainly be performed online and in real time, so if you add a static image, for instance, the libraries make it possible for a thumbnail to appear on the site or for the image to be resized automatically depending on the device and resolution which the visitor is using. Both ImageMagick and GD can be used with lots of web programming languages such as PHP, Perl and Python, so you don't have to stick to only one language to create your site. They work with over 100 formats, including the most popular ones - JPEG, GIF, TIFF, PNG, and so forth.