A couple of years ago you could still read the old Movie Talk posts and back in 2009 I found this advanced authentication technique described by "Huh" in 2005:
Look for text elements that look like they should be in black ink. One of the biggest give aways for a fake in my experience is black ink text. Whomever it is that scans or reproduces in other ways, a poster with the intent of creating a forgery, always seems to forget that black ink on things like text will only print in black, I'm talking mostly about credits and not any black that may be used as part of a graphic. Example of which would be a poster that I have that carries the GUI and NSS blurb all of which under a magnifier carry underlying colours which tells me that it was a re-scan and printed out of 4 colour process rather than being just printed in black as was originally intended....
