The Dogear-Nation team picked up on the fact that I bookmarked a description of the Picasa Name Tags feature for their episode 73. During the podcast the guys seemed to be a little confused about how this featture work and so I thought I ought to explain a little bit here.
For some time now, Flickr has had a feature called Notes. This works by allowing people to highlight a section of their pictures and then attaching a piece of text which will appear whenever somoene hovers over that part of the picture. This simple but powerful feature can be used in many different ways. One of the most common usages is that people use it tio record the names of people who appear in group pictures (e.g. see how I used notes to record the names of my former class mates in an old school picture).
Google's Picasa product is in many ways an attempt to immitate the more popular Flickr service (which belongs to their arch rival Yahoo). Until recently Picasa did not have an equivalent of the Flickr Notes service. Instead of simply copying the Flickr service, google decided to implement a service which is optimised for this use case of highlighting who is who in your pictures.
If you enable Name Tags on your Picasa account, then Picasa will automatically analyse all of your uploaded picture and search for any faces appearing in your pictures. Any picture containing faces will automatically be given a Flickr note type highlight attached to each of the faces.
The first advantage of the name tags service is that it automatically finds the faces and saves me the bother of having to highlight them myself. I find that it does this almost perfectly when people are facing the camera, but does not get things right when people are not looking at the camera (e.g. many of my pictures are action shots from football games). However, it does not matter if it makes some mistakes because I can always, edit the highlights and add more manually if I want to.
When reviewing my Picasa pictures, it prompts me to identify the people whose faces who have been highlighted. It provides type-ahead assitance based upon the names of the people in my Gmail contacts list based upon the assumption that the people towhom I send emails are also likely to appear in my pictures, but of course I can easily type any different name I want.
The really cool part of Picasa name tags comes when a person appears in more than one of your pictures. Picasa automatcially builds an index of your photographs based upon the people who appear in them. So if I need a picture of Joe Blogs to illustrate a story about him, I can just click on his name in the index to see all of the pictures in which he appears.
The documentation from Picasa seems to indicate that if I have enough pictures of Joe Bloggs in my photo collection it will then automaticically recognise Joe in my pictures. However, I have never actually seen this working (perhaps becuase I have only recently started using name tags and so I have not trained it enough yet).