I've spent a few hours putting a picture of a monkey through GIMP filters and scripts and then putting the final images into a webpage called monkey variations. The webpage includes three animations, which are also easy to do with GIMP. They take a while to load so you need to be patient.
This shows the power of GIMP (GNU Image Manipulation Program), which is an open source package.
I've prepared a worksheet about how to do this - both the GIMP manipulations and the styling of the webpage - and am happy to share it with anyone who asks.
Wara blogged last year about the idea of exposing students to free software first, that first impressions are important. Admittedly, the GIMP user interface is clunky compared to PhotoShop but what is under the hood is comparable, which is a great achievement given that GIMP is free and can be given to students to take home.
With respect to the filters and scripts I've heard that GIMP has more to offer because a variety of developers are happy to give something back to the community.