What I know about lithographs is limited to the 
ones that I have owned. All they are are very 
nice prints, probably done in some fancy way AND 
they usually have some sort of 'official' 
marking seal that determines how limited they 
are and such. I have seen them on cels, but its 
not at all painted, but most often they are on 
nice paper. Worth is determined by rarity and 
the demand. Also, the original price from the 
studio has something to do with it as well. 
Lithos of animated movies, I have noticed, do 
not show an exact frame from the film. Probably 
1 out of 10 are a reproduction /exactly/. I, 
personally, wouldn't pay more than $40 for a 
lithograph, and only for a show that didn't have 
cels in the first place, just because I know 
that 5000 /other/ people can hang the same 
picture on their wall. Lithographs that are fun 
to get are promos, because they are free. :) 
Like, for the Titan A.E. release and Vampire 
Hunter D, Suncoast offered free cel-style 
lithographs from those movies if you pre-ordered 
them. :) The Disney Store often does the same 
thing for their movie releases, but theirs are 
paper-style. Oh, and I could be wrong on all 
this, its just my opinion. Below is the free 
lithograph for Titan A.e.