u can host ur pics for free at www.imageshack.us
or photobucket.com or any one of several others. u just find some pics of what you like from google or yahoo or wherever and then u can upload them for free and link to them in ur signature or avatar.
photoshop is what most people use. u can also use jasc paint shop pro, www.gimp.org
, or just do a search for photo editing programs.