of such applications - some excellent, some good, and a lot not so good.
I regularly use an excellent program called PhotoImpact, which is superb
click here for more information about that.
Other forum users will have their own favourites, including Adobe Photoshop which I also use a lot.
Prices vary a lot, and if you're just starting out with image editing you might prefer to try a free program until you get the hang of things.
click here to take a look at a very popular download called Irfanview. It doesn't have the range of editing tools that you'll get with the heavyweight applications, but it's worth exploring.
For some useful background information about image editing take a look at this