Alrighty, first off, I asked what you should do 
if you paint a cel from a screen capture and then 
find someone that has the production cel/a cel 
that is very close to it.  

I did NOT ask 'hey, does anyone mind if I go rip 
off their cel galleries?'

Seriously!

THIS is my Ebay feedback profile, and it's got 
feedback from just about every cel auction I've 
done:

http://cgi2.ebay.com/aw-cgi/eBayISAPI.dll?
MfcISAPICommand=ViewFeedback&userid=gwenb@student.
umass.edu

If the images no longer work on that, you can 
check them off my website.  If ANYONE finds a cel 
I've sold on ebay that they have the original to 
of in their collection, I'll never paint another 
cel again.  THATS how sure I am that the stuff 
I've sold is legit.