I was just thinking about this picture in connection with the question of what kind of glasses they were actually wearing. I always thought that the glasses with polarizer lenses were an innovation of the 1980s 3D revival, but they weren't. Wikipedia, at least, claims that even during the original boom of the 1950s, most 3D movies used polarizer lenses and colored anaglyph lenses were used mostly for films that only had brief 3D segments.

It makes a certain amount of sense that both schemes would be in use: a polarizer setup requires special projection equipment (which, in its original form, was somewhat fiddly) and a particular type of screen, whereas an anaglyphic film requires no special equipment apart from the glasses, though the experience is inferior. Even today, home video releases of 3D movies generally use some sort of anaglyph scheme whereas theatrical movies use any of multiple polarizer processes.

Anyway, on my LJ I recently referred to this image as depicting an audience wearing anaglyph lenses, but on further reflection I'm not sure it actually is. In posters, book covers, etc. the photo is often slightly colorized: they'll draw in red and green lenses on the glasses to make it look like they're wearing colored anaglyph lenses. But I can't see any brightness differences between the lenses, though that's certainly not conclusive. They might be wearing polarizer lenses. Is it known what movie they were watching?