I had concluded that it would be Wrong to post 
cels in my gallery that had other people's 
specific watermarks.  Even if it were OK in 
principle, as a practical matter it would create 
a lot of confusion and misunderstaning if I had 
other people's watermarks in my gallery.

Then there is the question of the generic 
watermarks (like the "ipix" watermark from 
eBay).  My idea here is that these are ethically 
OK, but to be avoided if at all possible, because 
they make the cel look ugly.