I have a whole pile of photos of family and friends that I have indexed with Picasa v3.8 and it's face recognition ability, using the Windows version of Picasa3 (because it was the 'right' way to do this a couple of years ago).
In the middle of some facebook'ery using my preferred OS (Ubuntu 10.10 ATM) I decided I wanted a photo of a friend to post, so grabbed the Picasa installer and ran it up in wine. All went well, but I got a nice empty list of albums and no people, despite telling it where the photos are on the network file server. Time to find out where Picasa hides the metadata
Of course I went straight to the 'net and found a couple of posts back in 2007 that talked about copying album information from the Application Data area of the Windows user to the same area in wine's emulation: kudos to these guys:
The Hacking :)
A little prodding around on my Windows partition shows that pretty much the same structure is still there in current Picasa3 builds, along with the all important Picasa2/contacts folder that has a nice XML file with all my people in, and their Picasa hash values. These hash values are what ties together the contact details and the faces in photos, which are stored in special files (.picasa.ini), one for each folder through the image archive itself (on the file server).
I therefore copied the contacts.xml file, and the album XML files (from Picasa2Albums/<hash>) from my Windows disk to wine's emulation area (~/.wine/...).
The next trick is to convince Picasa3 that I have the same mapped drive letter (S:) in wine for the file server that I have in Windows - easy to arrange with winecfg.
The final hack was to open up the Picasa2Albums/watchedfolders.txt file and remove the slightly broken assumption that I have C:\Documents and Settings within wine..
Startup Picasa3 again, and lo! I have albums with photos in, but still no people. Bah. Just out of curiosity I tried adding a folder and Picasa did it's thing, scanning for faces and then oh joy reconnecting the faces with the contact details. So the fix is simply to rescan all the photos and it will pick up all the existing data (slowly). Time for bed while it chews through 10000 photos!