Picasa Name Tags

By default, Picasa doesn't modify your photos. All album organization, unsaved edits, thumbnail previews are saved on an internal database. That said, I know for a fact that captions are stored in the IPTC block, while GPS locations are stored in EXIF.

What about name tags? By default, name tags are stored in picasa.ini files located along with the photos. There is an option to write these name tags directly within the photo itself. Feature can be enabled under Tools > Options > Name tags > "Store name tags in photos". I believe this information is written in the EXIF block. Do note that this will only work for photos that have been tagged after enabling this feature.

With newer versions of Picasa, you can find an experimental feature that write these tags to XMP. Feature can be enabled under Tools > Experimental > "Write faces to XMP". You have the option to write face tags for selected photos, all photos that have face tags, or all photos regardless.