GIMP offers a range of tools and features that can help you improve your digital photos and the Levels adjustment feature can offer an easy way to tweak a picture.
If you've ever opened the Levels dialog in GIMP, it can look a little overwhelming, but it is a very simple tool to use. It doesn't offer the same flexibility as Curves, but for many images, it is just as effective a tool for making the most of a photo. The accompanying image shows a photo split in two with the right hand side showing the result of a Levels adjustment.