I've found a program called GIMP (Gnu Image Manipulation Program) that is by far and a way closest to Photoshop. And it's free. IMO, it tops Photo-Paint, PaintShop Pro, and PhotoImpact for image manipulation (retouching).


http://www2.arnes.si/~sopjsimo/gimp/

You want to download the run-time and the program itself, the top two items on the list. The Mac is not supported but if you scrounge this site, UNIX is also supported.


My Best,
Gare