You must photograph a total of 50 survivors throughout one playthrough. Here are some tips that will hopefully clear up any questions or confusion you may have:
- In the beginning, before the zombies break in, photograph the first handful of survivors. These DO count. Even though they die, their photos will still go towards the achievement.
- Group photos DO count. If you can get more than one survivor in a picture then you do not have to take their individual pictures.
- You can tell if a survivor has been counted as being in the picture if the circle highlights the person in the frame and their names appear in the top corner. If this does not happen for everyone in the photo when you take it, adjust your view or distance accordingly and try again.
- Photographing a psychopath DOES NOT count (except technically for Paul because when you defeat him and extinguish the fire and he joins you, taking his picture will THEN count as he is now classed as a survivor. The same applies to Isabela in that the photo must be when she is a survivor).
- Taking photos of rescued survivors in the security room DOES count. As in; if you didn't photograph rescued survivors when you first encountered them, it will still count if you photograph them afterwards in the security room instead.
- Remember to photograph Brad/Jessie/Otis/Barnaby/Isabela (as a survivor).
- And finally, don't worry if the photos you've taken of survivors start overflowing in the picture viewer and end up being replaced with new ones. As long as you've photographed the respective survivor(s) at all (in the same playthrough), you're safe.
- If a survivor happens to die on the way back to the security room, then taking a picture of their corpse will count, but it is always a good idea to photograph a survivor the moment you encounter them, just in case.
- The achievement will pop after the 50th survivor's photo--you will not have to wait until the end of the game.
Thanks to the people who commented with questions. I hope you found this information helpful.