how do you transfer pictures onto a cake

What kind of picture? If it is a photo of someone you can have an edible image made at walmart for $6.50. If it is a picture of a charcter you could do a frozen buttercream transfer. There is a tutorial on here for that. HTH!

You could do a Royal Icing Transfer. Here's a link to a thread with a great tutorial on the 2nd page of the thread.

http://www.cakecentral.com/modules.php?name=Forums&file=viewtopic&t=648450&postdays=0&postorder=asc&&start=15

Here's a link to the frozen buttercream transfer Tiffany mentioned.
http://cakecentral.com/articles/73/how-to-create-a-frozen-buttercream-transfer