After you finish a race, select "replay", and then again to play the replay.
to bring up the replay menu, where you can click on the icon to the right of a camera, titled "Race Photos" -
again to enter Photo Mode.
to select any camera angle (or walk mode).
to capture the photo. Back out once it's loaded, saving it is up to you. I moved the thumbsticks around once everytime just to make sure (not sure if it really matters), and
to shoot again. Rinse and Repeat x 100.
I wrote down 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 on some paper, and crossed each one off after i counted 10 shutter sounds for easy tracking. Trophy unlocked without any issues