I think I got the answer!If you want to export Face Detection you must copy your photos with picasa.ini or .picasa.ini which stored in pictures folders. And copy DB3 Picasa database (In Windows %USERPROFILE%\Local Settings\Application Data\Google\Picasa2 in MAC /Users/%USERNAME%/Library/Application Support/Google/Picasa3/db3/Picasa) on startup will clean in up and you will have faces on photos
@jasondunn: Try removing and then re-adding the folder where your
photos sit in Folder Manager. This will force Picasa to rescan all
your images, pulling the face tags out of the .picasa.ini file.@ptyork:
All your contact data is stored in db3\contacts\contacts.xml. If you
copy this file from the source computer to the destination, you’ll have
the same contact information. This information, combined with what’s
in the .picasa.ini file is really all you need to transfer your
facetags between computers. That said, the better solution is to use
Google Contacts
via How to Back up Name Tags and copy to an another compter – Picasa Help.