Over on SitePoint.com today, there's a new tutorial demonstrating an alternative to the usual GD library examples of working with images, opting instead for ImageMagick.
The key component for making dynamic images a reality on your site is an image manipulation program that's controlled by the code that generates your web pages. Even though this article uses PHP as the scripting language, other languages -- such as Perl and Ruby -- can be used just as easily, provided that the image manipulation program that you're considering has an application programming interface (API) for the chosen language.
He decided on ImageMagick for a few reasons, including that it's more supported by web hosts, it runs on Windows and Linux, and it's robust and powerful enough to handle everything from small to large tasks without missing a beat.
That said, he gets into the code, showing how a bit of PHP code can read in an image and spit back out information about it (height, width, etc), force a reduction of an uploaded image, scale down an image to fit a certian size, change it to a different type of image, and image rotation.