Within the Prometheus trailers and TV commercials, there are certain anomalous frames of what appear to be heavily distorted, blue-tinted video.
I believe that many, if not all, of those frames are from the original Alien film.
When the three Nostromo crew members approach the derelict, Ash is watching them from the ‘science blister’ via video.
This video footage appears to be taken from or by one of the suits.
Stepping through those scenes frame-by-frame, and referring to the Prometheus wiki, I have found multiple matches of the Alien video frames to the Prometheus frames.