Optional mode: Grey out or mark photos you've already viewed#618

It would be nice to be able to temporarily turn on a mode where all the images you’ve already viewed (clicked on) are somehow greyed out or somehow marked, to be able to quickly take a look at what you’ve not engaged with yet.

It would be best if this mode would work in all the views, especially in a person’s “Photos” feed, as you might want to see at a glance how far you already checked out their feed. It would also be nice when looking at the “Following” and “Followers” views, to at a glance see if the person is someone who’s photos you’ve already looked at.