I've been using The GIMP since 2005. I first used it in a Linux distro. Later that year I found that The GIMP was "Open Source", which means the "source code" (Original program code) is public and is under the GNU licensing agreement. Anyone can modify and improve the program. Or "port" it into a different Operating System so it runs under Macintosh, Windows, or even Unix.

That is perhaps the best feature of The Gimp. Photoshop is better but with The Gimp I can use whatever Operating System I'm using at the time. The Gimp is exactly the same on every platform, so I don't need to learn multiple software programs.

I do all my photo processing with The Gimp. It is easy to learn and is being improved with every release. The latest major improvement is an image window that stays open and you can "drag and drop" images to be processed.

One of the best of the Filters, under the "Filters" Menu/Enhance is the "Unsharp Mask", which is a simulation of the photographic process of unfocusing a negative slighly and then sharpening it. The "Unsharp Mask" does a great job of sharpening photos in a clean way. Then there is the "redeye" removal and plenty of others.

The Gimp is great for cropping, resizing, and all the other image processing that I need to do. You can get The Gimp for Windows, Macintosh and is included in most Linux distributions

There is also good support for Graphics Tablets (Wacom is the best) and advanced features such as layers and animation. The Gimp works with almost all image formats including the native Photoshop (psd) and it has other features.

The best thing about The Gimp: It's free.