There are only a few free good image editing programs available on the Internet in my opinion. Some of these programs are easy to use but have limited functionality, and others are more powerful but the complexity of using the program increases.
One you might want to check out is PhotoFiltre, it’s powerful and easy to use. Here is an excerpt from their web site: "PhotoFiltre is a complete image retouching program. It allows you to do simple or advanced adjustments to an image and apply a vast range of filters on it. It is simple and intuitive to use, and has an easy learning curve. The toolbar, giving you access to the standard filters with just a few clicks, gives PhotoFiltre a robust look."
PhotoFiltre is free for a private, non-commercial or educational use (including non-profit organizations). Commercial or professional use requires registration.