This is actually a AIBU for DH.
DH feels extremely strongly about photos of the kids on social media. He has worked in cyber security and always knew that he didn't want pictures of his kids online (including shared by non secure message like whatsapp). It's been a pain in the backside, but I have supported him on it - never send pictures around or posted them anywhere. He found a secure messaging app which would allow us to share pictures with family and friends but which did not allow the pictures to be shared or stored. He set this up for anyone who wanted it and we've managed fine for 3 years.
MIL didnt want to use the app. So we have been printing off and giving her pictures of the kids whenever we see her, and also sending regular pictures in the post during lockdown.
DH recently sent a family friend a message congratulating them on the birth of a grandchild. The family friend replied saying thank you and "it has been so lovely watching your kids grow up from afar" (they live in Australia).
DH doesn't have Facebook so I searched for his mum (we aren't Facebook friends - I also don't really use it). His mum has been taking pictures of the hard copy photos we've sent and posting them on Facebook, freely viewable to all (no privacy restrictions). She has uploaded literally hundreds of pictures.
DH has explicitly explained why he doesn't want pictures online to his mum. He confronted her about it and she shrugged and said "I have to be able to show off my grandkids". He is spitting mad and has said he will never give her another picture, to which she has kicked off massively. IHBU?