Theres a new way to tag your Flickr photos to indicate flickr users are appearing in them.
Quite a few users have already started doing it. The way it works is to use the following "machine tag" notation, for each flickr user in the photo
(replacing [flickr-username] with the username of the person in the photo)
e.g. if there were 2 flickr users in my photo, lets say their flickr usernames were fred11 and joe44 you would add the following 2 tags to the photo: flickr:user=fred11 and flickr:user=joe44
I made an rss feed of the flickr:user=* tags, which you can access here: feeds.feedburner.com/FlickrUsersInPhotos
to list the photos with flickr users in them. The feed is GeoRSS enabled, which means it adds the latitude and longitude values to the item, if the photo has been geotagged. And lets you do things like viewing the feed on google maps. I also just found a GeoRSS to KML converter, so heres a KML version of the feed, for the Google Earth fans.
if you wish to be notified when you are added to anyones photos, you can simply subscribe the flickr provided RSS feed for the flickr:user=yourusername tag in your news reader application.
theres also a greasemonkey script written by jacobd with some additional code from me, that detects these tags, when you are viewing photos on flickr, and adds user icons, usernames and links for each tagged user in the photo, next to the photo. It also activates the buddy menus for the icons and adds a simple way of adding the user tags, via a select box populated by your contacts list.
You can get the script here: flickr.users.in.this.photo.user.js
Theres more discussion on this topic in flickr central.