Often people will have a their photos on more than one computer. They may have a main home computer and then a laptop and maybe a spouse or child will have yet another computer or two. The problem with this is before long the same photos will not be on all the computers because each person may take photos and import them to their own computer.
Here we suggest a way to get all the photos onto the main computer so they can be saved and archived in one place. With all the photos backed up and in one place the other computers can copy the photos needed and know that there will always be a copy if something happens to their Laptop or whatever.
Pick one Computer to be the Master computer. It will probably be the main desktop PC with the most speed and storage.
Make sure Picasa is updated to the latest version (Version 3.9.141 build 259 at this writing).
Make sure indexing and scanning is complete so the database is up to date
If using face tags it is suggested that the face names be in the photo metadata as outlined in this FAQ:
https://sites.google.com/site/picasaresources/Home/Picasa-FAQ/picasa/general-information/where-does-picasa-store-facetags
Once the above is finished, then exit Picasa so the database will be up to date.
Get an external drive large enough contain a backup of the complete photo collection on the master computer, and in addition a copy of the complete photo collection on the computer to be merged.
Create a folder on the external drive called something like "Master Backup", and one called something like "Slave Backup".
Using this FAQ methods steps 1 and 2, make backups of the Master computer all photos and database into the Master Backup folder:
Using the same FAQ method, make a backup to "Slave Backup" of the first computer to be merged into the Master.
On the Master computer, make a folder inside the Pictures folder called " Old" or something recognizable.
If you have the room, copy all the photo folders from the Old Backup folder to this Old folder (Don't Move, Copy).If you don't have the room, copy some of the folders, and do the steps below, then copy more folders until you have them all.
If you have People face tags, the steps below may improve the number of faces that stay named on the added photos.
Do these steps the first time you copy the photo folders from the slave backup to the "Old" picture folder.
Go to Slave Backup and find the Database \Google\Picasa2 folder.
In the Picasa2 folder, find the Contacts folder and in it find the Contacts.xml file.
Right-click on contacts.xml and select "Copy", then click anywhere else in the contacts folder and select "Paste".
A new file called Contacts - Copy.xml should appear.
Right-click on contacts - copy.xml and rename it to Backup.xml
Copy this Backup.xml file to the database Picasa2\Contacts\ folder on the Master PC so it now contains the both a contacts.xml file and a backup.xml file.
Start Picasa on the Master PC and wait for it to scan and index all the new photo folders.
(Note: It will then start Face scanning, you don't need to wait for the face scan to finish.)
Remove the duplicate photos and folders using the methods in this FAQ:
Look through everything remaining in the "Old" folder and it's subfolders and move everything remaining to the folders in the Master Pictures folder.
After Old and it's subfolders are empty it can be deleted using Windows Explorer.
Repeat the above steps for the "Older Backup" folders.