Hmmm . . . I'm very confused.  I might be 
sending some letters/emails around to try and 
figure this out.  My mom has a law degree so 
maybe she can help me.  So, I always thought 
that if you owned a piece of artwork such as, 
lets say a painting by Van Gogh, then you do 
have the right to reproduce the image because 
the image and painting both belong to you.  Who 
else would have the right other then you?
But when it comes to an animation cel . . .  
Still, the studio did sell the cels.  They could 
have chosen not to if they didn't want the image 
used at all other then by them.  However, it is 
true that they own all rights to the show itself 
and the character but, I really can't see how 
the owner of the actual cel would not own the 
image itself.  Even to the point of reproducing 
it . . .
Well, I'm going to talk to my mom but, I'll be 
back to this thread later if she says anything 
enlightening.