Flickr offers a variety of “machine tag” options that can be used to link photos to data on other sites, such as upcoming.org or openstreetmap.org. Using those tags, it’s also easy to link your Flickr photos to Foursquare venues.
Simply tag the photo with “foursquare:venue=XXXXXX” where XXXXXX represents the venue ID (the numbers at the end of the venue URL) for the location where the photo was taken. Flickr automatically adds a link to the Foursquare venue in the “Additional Information” column. For example, this photo is tagged with the Foursquare venue where it was taken.
These tags make it easy to find photos from a venue by searching for the appropriate foursquare:venue tag. You can also search for all photos tagged with a Foursquare venue.
Right now, Foursquare hasn’t used these tags to incorporate tagged photos into their venue information, but they could easily add that integration. It would provide a simple way for them to add the often-requested venue photo option by leaving the cumbersome task of storing photos to someone who specializes in it.