Oh, something I actually know something about as I was working with people choosing pictures for the gravestones and/or funerals..
There are no strict rules, but I always saw the tendency for going with voices of the family “he looks really handsome on this one”, “yeah, that’s her face, you know, she always looked like this during the fall, her favorite part of the year” and so on.. This might not be helpful but the best one is the one representing the connection as much as possible.
I have this strong feeling after so many of those — sometimes very unpleasant — talks, that anyone that has to choose, already made that choice internally, they mostly just don’t want to make it officially, as it is making the loss and whole situation even more real.
It is mainly for everyone mourning, a form of expressing how they want and need to remember this person. I would go with the one that pulls the string inside “yeah, that’s them, that’s how I see them”.. Most often, that picture was actually making people smile, cheer up, even if through the tears, that was the sign for me that we have the best one.
Bunny Lake Is Missing (1965) — hard to say anything without spoiling the plot
Blair Witch Project (1999) — I just admire how great idea / concept extended beyond the movie itself. No-one can ever watch it again for a first time during ‘99 but it is iconic and great as a case study of having almost no budget and making something really impactful / special
Her (2013) — this one is my answer for the same question but asked in 2061..