When you use Bridgy Publish to POSSE a photo post, it should read the person-tags from the original post, and propagate them to the POSSE copy (e.g. to Facebook or Twitter).

Original question/request: http://indiewebcamp.com/irc/2015-09-01/line/1441139069479

See also:
http://indiewebcamp.com/person-tag

This could be implemented in at least a couple of steps/iterations.

Phase 1: only use person-tag URLs of silo profiles that are directly indicated in the h-cards of the person-tags on the original photo post. E.g. a person-tag h-card could have multiple u-urls on it, and if one of them happens to match the silo domain, use it as the identity to person-tag on the POSSE post! (I'll add an example of how a person-tag publisher could do this to the indiewebcamp wiki to hopefully make it more concrete).

Phase 2: look up the person-tag's silo profile equivalent via rel=me identity lookup on their website. This would require Bridgy to retrieve the first u-url of the person-tag h-card, parse it for rel=me links (i.e. use a microformat2 parser), use the first one of those rel=me links that happens to match the silo domain as the identity to person-tag on the POSSE post! This could require Bridgy to do one additional HTTP(S) request per person-tag on a post which thus depends on the number of people in a photo.