This Seeking Tech tutorial will explain how you can unlock the Memento trophy in Ghost of Yotei. You can do so by taking the following steps:
Step 1: Make sure Photo Mode is turned on for the game.
Step 2: Open Photo Mode during gameplay by pressing on the right directional pad button.
Step 3: Afterwards, use Up and Down d-pad buttons to select a personalization option.
Step 4: Finally, use Left and Right d-pad buttons to unlock the trophy.