You can go any way you like. If, for example, you 
have a cel from DBZ of someone fighting at the 
Martial Arts Tournament and you know someone who 
has a background of the crowd for that scene, you 
can ask that person to email you a scan of the 
background. Then just take it to Kinkos or 
something and print it out on matte paper 11x17. 
Or, you can find a screen capture, blow it up to 
size, and have it printed out. The one below was 
taken from a screen capture. It matches the 
episode, but it isn't actually from that scene.