I just want to point out that IMHO, it's much 
harder to be sure that a cel is real then what you 
make it sound. Even if you can hold the cel in 
your hand... much more if all you have is a scan.

I think that the number of cases there was lately 
with those Anisoft copies is proof enough.

Matching a picture with a screen capture of the 
anime can only be done seriously if you have an 
old analog LD player. Using a DVD, tape or digital 
LD player isn't enough as not every frames are 
recorded, many frames are a composit of 2 other 
frames and compression algorithm are losing data 
and changing the picture. It's inherent to the 
process used to record on those media.

Sure, sometime you can catch some "well-known" (
sort of) copies like those Anisoft or AMG repro 
cels. But to my knowledge, I am the only person 
that try to make a list and as I mentioned several 
time, I know that those lists are incomplete.

There is plenty of cases when it is obvious that 
they are copies. But there is also a fair number 
when it is far from being obvious.
Also, nearly the only proof you can have is a 
negative one : It is often possible to be sure 
that a cel is fake. But you ca