DS9Sega said:
That's been debunked a number of times. It looks like a silhouette of Vader for about one second, but what you're seeing is simply a dark gap between parts of the "data pattern"ed Epsilon Nine station. A moment later, the illusion is destoyed.
It was debunked?
Darth Vader and Miss Piggy both get cameos - as reflections in Spock's faceplate, IIRC. The SPFX guys pointed these out in interviews at the time.