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.
Here's a link to the frozen buttercream transfer Tiffany mentioned.