Cels Forum

To fully protect a background and a cel, the best idea I've
come across is to put the cel and the background into
seperate cel bags.  Or to put the cel in one bag and then
the cel inside the bag with the background.  

Like was mentioned before, laser copy background generally 
don't increase the value much more than the cost of making
the copy.  There are some studio ones, which are easily 
distinguished as they are on different paper, and usually 
have some kind of seal from the studio.  Those will 
increase the value of the cel marginally, but not nearly as
much as the real one.