photochopping is done w/ a photoediting program such as adobe photoshop or anything like that...
it takes a lot of practice to do, but basically you can take tidbits of pictures and combine them to make a different picture....
for some examples:
1.) check out the picture in my signature.. thats 3 different pictures of my monte and a diff background combined together and then words overlaid on top of the picture
2.) check out my avatar... thats also a photochop where someone highlighted the outlines of a monte carlo and used just those as a picture
3.) this is another photochop where a cple of girls heads are put on top of the powerpuff girls bodies.....
if you'd like some more examples just search "photochop" on google image search.... if you'd like someone to make a photochop of your car to put in your signature or use otherwise... post pictures in a new thread here... or email them to me and ill c what i can do