Although this is for photographic, you can do some amazing things with photos. If you treat them as images you can import them to a 3D program as an element in a landscape or into a 2D program to apply painting textures or framing elements for webpages.
Below is a list of links compiled on another forum I am on. I hope you will find some of them useful.
Most of the stuff here is for photo-manipulation, but even if turning Catherine Zeta-Jones into a cyborg isn't your thing, you can learn a lot about HOW Photoshop works by following along with the tutorials.