Lemmy Support

I'm running an instance for me and a couple of friends at https://lm.put.tf/. I've noticed that there seems to be no consistency whether or not post images are mirrored in instance's pictrs

For example:

The post https://lm.put.tf/post/22176 from !lemmyshitpost@lemmy.world has its image mirror from https://sh.itjust.works/pictrs/image/92ec8e81-1f05-4ff7-8ec7-f3bdee3d8087.jpeg to https://lm.put.tf/pictrs/image/747826a6-281f-4b1b-8ba2-7bbf452916dd.jpeg

However the post https://lm.put.tf/post/22060 from the same community, but posted by a user from lemmy.blahaj.zone does not have a mirror on my instance. The image links to https://lemmy.blahaj.zone/pictrs/image/OpIT86L1vq.jpg

Why is there a difference in behaviour? is it because the post was done from another instance and not lemmy.world? What is the replication/mirroring logic?