"Mark As Spoiler" Feature

Theres times I am talking with my friends and we are sharing images
These images arent NSFW in any way, but that doesn't mean they aren't always disturbing to some extent (especially when it comes to things like distorted faces)

I think it'd be useful to have an option to personally mark an image or message as spoiler, so that if you don't want to see it you wouldn't have to.