Kudos to Crash for solving the mystery mask photo.
A photo of a mysterious yellow hock has been around the fan community for a while and no one seemed to know the story behind it. The mask was so intriguing because it was clearly old, apparently on a part 4 hood, and had characteristics of masks from several films, including inverted part 5 chevrons, a triangular part 6 style forehead chevron, part 4 eye cuts and part 6 style straps. Strange indeed.
Some had speculated it was an unused design from part 5; it appeared in a promo video for Friday the 13th part 5 as seen here. Note the dirt patterns on the left side of the face match perfectly, identifying it positively as the same mask. So we can say for certain this is indeed a sister mask to those made for one of the films.
Crash has concluded its likely to be a spare from part 3, and thus one of the original hocks produced. Given its slimmer appearance, larger eye cuts and 3/8 holes, this is entirely possible, although the fact that its photographic history as far as we can tell goes back to part 5 seems to suggest it could have been part of the "Roy" set that was produced for that film in 1984/85. Either way, its an interesting find.