When someone blackmails you with an embarrassing or bad photo of you don't reason with them to delete it try pushing the person grab there phone and break it that's what I would do anyway.
I think mostly they could access it if they log in with a new phone You need to delete it from their google account/whatever iphon has(never used an iphon idk)
When someone blackmails you with an embarrassing or bad photo of you don't reason with them to delete it try pushing the person grab there phone and break it that's what I would do anyway.