Picasa is a free photo editing software from Google. You download the software to your computer and you can edit and touch up your photos. Picasa also has an online component, Picasa Web Albums, to share your photos with others. I've found it to be easy to use and very powerful. I have used it myself, and I have my students use to modify pictures or graphics for projects.
You can learn more about Picasa and Picasa Web Albums HERE.