On typical photo silos that you can POSSE to (Facebook, Flickr), in addition to liking & commenting your friends can tag people they know in those posts.

On Instagram, you can add person-tags to your photos after the fact as well as during posting.

Bridgy should backfeed these silo person-tagging interactions just as it backfeeds comments for reasons that are helpful to the publisher particularly for photos:

https://indiewebcamp.com/photo#backfeed_person_tags

Originally requested: http://indiewebcamp.com/irc/2015-09-01#t1441140760078

Bridgy can do this by creating synthetic tag-reply posts (similar to reply posts), with "tag-of" markup and person-tag "u-category h-card" markup as documented here:

https://indiewebcamp.com/tag-reply
https://indiewebcamp.com/person-tag

And then send a webmention back to the original post like the existing Bridgy backfeed support.