Photo Editing With Picasa

For DJ's FLVS Photography class, he had to take five pictures he took and edit them using whichever software he wanted. Since I upload most of our images to Picasa, he used that one. The first set of images are the originals. You can see the striking difference once they were edited. I was amazed at the difference. We don't generally edit our pictures. I try to get him to learn to take good pictures naturally, but wow what a difference! I have been adding watermarks to his images, the really good ones, that he wants to save. But, it is very time consuming. These images belong to DJ. No one is authorized to borrow or use them for any reason. Do you edit your photos? Which program do you use?