Face Recognition

Last night, I checked out the efficiency of Picasa's facial recognition for automatic tagging. Its performance was rather impressive. This particular technology was added sometime in September 2008. Currently I have about 32 albums in Picasa and the system automatically identified 853 faces in it. It must be mentioned that not all the faces were distinct but in all I think its a decent job. Judging by performance in the engineering sense, it may not be very impressive but in terms of convenience and regular use, it is quite helpful. I tagged about 200 faces in less than 5 minutes and this covered several thousand photographs in all my albums.
What was really impressive was that it never misclassified any of the faces. The faces of the same person was always grouped together. However, not all the faces were put in the same group even though they may have been in the same orientation or lighting condition. Thus, I feel that the algorithm working behind this technology is more geared towards avoiding false alarms. I wonder what kind of algorithm might be used here. I tried to search for the algorithm but so far haven't found anything that reveal the actual working of this tool.
Though I haven't worked with facial recognition, I have had enough experience in speaker recognition to appreciate the difficulty of such a task. With millions of picture present in Picasa albums, its really a great way to check the statistical performance of the facial recognition method.