Photoshop has been the mainstay of image manipulation for some time now. As with most soft the general public has taken it and used it for their own purposes, hence the Photoshop Contests. Many forum type websites have had contests among their members challenging them to "Chop" an image. This has progressed to sites dedicated to photo manipulation. The members are given a theme or an image and have a set time to do their magic. These contests mostly are for fun. One example site is [404 Check: was link to chopncrop. com, anchor: Chop N Crop] . This site is just for fun but as membership grows monetary prizes will be ocassionally awarded.
The popularity of this hobby has led to the developement of a few FREE programs that are quasi-clones of Photoshop. Gimp and Paint.net are two examples of free software that are becomming very popular with the image manipulation hobbiest who does not want to fork over several hundred dollars for software.
If this sounds interesting to you, or you just want a few laughs here is a link to a few images that have been "chopped" just for fun. Funny Images A google searcg for photoshop contests will also give you many pages of similar content.
One additional note: most of the sites that are dedicated to image manipulation also have great tutorials and other resources.