Photographs in Actor Filmography?

I have noticed a rather weird tendency of photograph appearances either disappearing from the acting filmographies or receiving "(credit only)" treatment. I don't know whether some SAG-AFTRA  standards are in play here, but I wonder whether cases in which photographs were actually made for the movie, as it is with Alfred Hitchcock in Lifeboat (1944) or Bruce Davison in Willard (2003) might still be listed. Technically, actors worked for a day showing up for a photo shoot (and in case of Hitchcock he was actually photographed twice for "before" and "after" photographs) which still should be listed (unlike the use of pre-existing photographs). 

There are also borderline cases - Liza Minelli is now listed as "credit only" in The King of Comedy (1982), because she only appears in a cardboard cutout in the movie, but it might as well have been "scenes deleted", because she had actual scenes shot, which were eventually deleted and that is the main reason why she has a cast credit.

So what are the rules in cases like that, or should it be decided depending on case? I should say that I have a few acting credits which are actually photographs, but they were credited and specially comissioned for productions.