My take on the subject is that as long as you are 
not promoting the cel as a production cel and 
rather as a fanart cel, then there is no 
conflict. It's not like one of those situations 
where someone blatantly takes an image from a 
gallery and promotes it as their own personal 
property. You are simply doing a reproduction and 
are stating it as such, instead of passing it off 
as an original production cel.