The Gimp program is free http://www.gimp.org/
I have never used it, and here that the learning curve may be considered steep, but some artists seem to like it fine.
Sign Up or Login and this ad disappears! There are many great features available to you once you register. Sign Up for a free account and browse the forums without ads.
There are many great features available to you once you register, including:
Sign in or Create Account