To unlock this you have to complete Act 1 without dying. Despite what the achievement says you don't have to fully finish the game, the achievement pops right after clearing Act 1.
There are 2 major points you can potentially die imo
- first is the scissor ghost boss fight, this can either be really easy or incredibly bs.
Either your camera will glitch leaving you unable to take photos, or the ghost will consistently spawn inside of you. I'm not sure if there's a strategy to make this less luck dependent. I believe it takes 7 or 8 photos to defeat it.
- second is after you take the school keys from the pig and go down the hallway toward a bunch of bugs. After walking through the bugs you will be teleported to another hallway, there will be a ghost slowly coming toward you. This ghost will one shot you if you get grabbed. Walk down the hallway a bit, looking at the doors on the left with your camera. One of the doors will be hidden and will only be visible on your camera, once you find it, walk through and you should be safe.
I was gonna put the lady in red as another somewhat difficult section but she's incredibly easy. Avoiding her is not that difficult at all except for the rat phase, i always tank a hit and run past her during that one.