ImageMagick and GD are software libraries which should be present on a hosting server in order for images to show up on a certain site. They allow you to execute a variety of tasks with the images - create, flip, resize, change colors, etcetera. These things can certainly be done online and in real time, so if you add a static image, for instance, the libraries make it possible for a thumbnail to show up on the site or for the image to be resized automatically depending upon the device and resolution the site visitor is using. Both ImageMagick and GD may be used with a lot of web programming languages like PHP, Perl and Python, so you don't need to stick to only one language to build your website. They work with over 100 formats, which includes the most popular ones - JPEG, GIF, TIFF, PNG, etc.