Landmarks are one of the collectible things to find in Marvel's Spider-Man, but in contrast to most other things, you don't have to physically collect them, and all you need to do is to snap a photo of them. You get a very short introduction to taking pictures of Landmarks early on in the game, but a lot of people (myself included) had problems with doing it once you are out in the open world and ready to get those photos to get Landmark tokens.
So, here's how to take a picture of a Landmark in Marvel's Spider-Man: Press the Up button on the D-pad to open up the camera menu. Now hold down L2 to zoom in. Now hover the center of the camera over the Landmark, and it will tell if if you got the Landmark shot or now. Once you do, just click on R1 to take the picture.
You usually don't even have to be particularly close to the Landmark to be able to snap a photo of them. Just get them in the center of your camera lens, and you should be good. Tall buildings and bridges can be photographed from very far away.
Landmarks are found all over New York, and each photo awards you with 1 x Landmark Token. These can be used to purchase new Suits, upgrade your Gadgets, or upgrade your Suit Modifications.