Pleroma when receiving a picture from Socialhome: let's show it twice(*), just in case.
Pleroma when receiving a picture from Friendica: let's show it three times(**), must be important.

(*) once the inline picture, again as the attachment, because it doesn't recognise the picture is already shown inline.
(**) same, but also as link preview because the Friendica inline preview image has a link to the full image, which Pleroma thinks it needs to generate another preview for.

(I understand how this happens so no complaint, a rule like 'don't show an attachment already shown inline' was never claimed to be implemented and may not even be possible. That Mastodon correctly shows the picture once is just because it can't show inline images at all)