Photo Mode is a tool, which will give your players an ability to capture screenshots of their gameplay moments.
You can also use it to make stunning pictures of your game, which will help you to promote it.
To use this mode you need to add BP_PhotoModeManager to your player controller and bind keys for "Activate/Deactivate Photo Mode" methods.
When you enter Photo Mode, the time is stopped, so you can fly around and capture even short, but gorgeous moments.
In Photo Mode you can adjust the final screenshot: change Field of View, Depth of Field, apply filters and much more.
You can also easily extend this mode to add your own controls and filters.
To use cinematic DoF in UE 4.23 and above, you need to set post-processing quality to cinematic in engine scalability settings.