I did not know until now that it is possible to embed external images within posts and replies. I thought the only option was to upload to your instance.

this is bothersome, but if you use a VPN then at least there's that.

otherwise it's feasible to track captured addresses based on which posts they read by posting an external image in the post or a reply.

if you are seeing images in this post, then your client address is visible to any external image hosts.