You'll get this achievement during episode 4, you need to find and photograph these 3 items;
• Kate's plane, she's playing with her plane in front of you.
• Charlie's guitar, he's playing it further along the beach.
• Locke's wheelchair, you'll find this at the jungles edge on the beach, it's covered up a little by some vegetation.
I've also linked in a video which will show you where to go to find all of these.
* Credit to SaggDog7 for the video