GIMP is the GNU Image Manipulation Program. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages.
http://www.gimp.org/I've used this a number of times when manipulating and creating graphics to use on the forum. It is a full featured image editing program that has the power of Photo Shop without the heave price tag.
If you decide to try GIMP, let's use this topic to ask and answer questions about it's use and features. I use it some just not enough to be an expert on it.