In the latest PlayStation blog it read, "Fans expressed an overwhelming desire to see and share the realism, beauty and detail of our Neo-Victorian world. With Photo Mode, you'll be able to compose, capture, and share stunning images of your favorite moments, characters, and environments."
On top of being able to take great shots of your gameplay by heading into the photo mode at any time, there are a number of settings within photo mode that apply to your own game experience too. You can adjust some of the color gradients and other graphical settings to change the appearance of your game in real time. For example, if you want to play with a sepia tone, or want to see what playing The Order: 1886 in black and white feels like, you can set these things up in the photo mode.
"Since The Order: 1886 is completely rendered in real-time with no pre-rendered frames, you're able to play in a customized look from beginning to end. If at any time you want to change Color Grading styles during gameplay, simply enter Photo Mode and make your adjustment. You can also reset the option if you wish to play the game as it was originally intended."