The GNU Image Manipulation Program (GIMP) is a free (as in freedom as well as as in beer) software program that does a large amount of what photoshop does. Because it's free software you also get the right to see, study and improve the source code, and share copies of it provided you pass on the same rights to others. Download it from:
http://www.gimp.org/

HTH
Charlie

--
Don't Stand on your head - you'll get footprints in your hair
                                           http://charlieharvey.org.uk
                                              http://charlieharvey.com