From Sander van Zoest at Uncensored Interview, a convention for representing MusicBrainz identifiers using Flickr’s Machine Tag mechanism.
Example:
A photo of Matthew Dear, tagged as follows:
musicbrainz:mbid=3d191c12-be64-4f90-94d8-ac324b2b3544
wikipedia:en=Matthew_Dear
It also includes a Wikipedia identifier which could be used to link to DBpedia (though this might duplicate information also available within MusicBrainz’s advanced relationships system). There must be many 1000s [...]