Immortality

The basics which you likely already know if you've been playing the game for a bit: when viewing a scene click Y to go into Image Mode, where the cursor becomes a small circle that will have an eye symbol in it when over objects that can be clicked on with A.

Ruby is the Asian female police officer in Minsky, one of the fictional films being made in the game. She appears in a number of scenes. This achievement should pop after clicking on her in 3 different scenes.

Some of her appearances in chronological order:

MINSKY 7 - 6/23/1970
MINSKY 31 - 6/26/1970
MINSKY 8A - 8/4/1970
MINSKY 3A - 8/11/1970

The above list likely isn't exhaustive as I am still working my way through the game.

Clip names can be seen on the Film Grid, which is one of the views you can see when backed all the way out of a clip using the B button. There is also the Image Grid, which is a collection of shots of the objects you've clicked on. The two views can be switched between using left trigger.

It seems a lot of scenes can be found in various ways. Currently I'm not sure you could say "Click on A to get to scene 37." as clicking on the same object in the same clip can take you different places sometimes. But once you have found your way into one of the fictional films you can find a lot more scenes from that film by clicking on the actors and crew in the clips you find. Other than Marissa Marcel and the DP of Ambrosio/director of the other two films, the cast and crew seem to be unique to each movie. EDIT: as pointed out by Irrotational in a comment, there is at least one actor who appears in both Ambrosio and Minsky, so the casts other than Marissa Marcel aren't totally unique to each film. But for the most part clicking on faces is still a good way to find other clips from the same film.