Star Trek Beyond: 25 Easter Eggs, References & In-Jokes
7. The Original Cast "Cameo"
Right at the end of the film, Spock is once more reflecting on the life of Ambassador Spock and his own decision to leave the Enterprise, while going through his personal possessions.
He comes across a photograph of the original crew from later missions, which seems to be the straw that breaks the camel's back for him and he decides to stay with the ship. The photograph is actually a cast photo from Star Trek VI: The Undiscovered Country (1991).
Again, it's a very bittersweet tribute, but a wholly fitting one.