I use GIMP. It's free and it's still maintained I think. There is a help manual online but it took me a while to work out how to do what I want. You can do amazing things with it if you want to and are interested enough to learn. I don't do anything too clever, I've been scanning all the family photos - it is good for correcting old colour photos that have gone yellow over the years, cropping unwanted bits and resizing things. I even did a bit of surgery on a cousin who had lost part of his head by replicating the hair on the other side of his head and pasting it and correcting the colour.
