Free Image Editors for Everyone--Even Experts

I can certainly recommend gimp. It took a little effort to get used to, but was OK.

I also recommend Corel paint shop pro. I found an old version for free.

I use Photoshop myself but if I was starting from scratch I'd pick whichever program was easiest to learn. That's because it took me five years to learn how to use Photoshop and sure, with a lot of effort it can produce professional-looking results but just imagine much stuff I could have produced in the meantime while I was learning how to use it.