Using Name Tags (Face detection)
Picasa has face-matching technology that lets you organize your photos according to the people in them. Name tags are turned on by default, so the first time you open Picasa, it will use face-matching technology to scan your photos for new faces. This page also discusses how to delete name tags.
How to use the Picasa name tag feature
More information: Keep your People Named by Checking this Box
Adding name tags to faces lets you organize your photos by the people in them.
In Picasa, click Tools > Options (for Windows) or Picasa > Preferences (for Mac).
Click the Name Tags tab.
Place a check mark in the box "Enable face detection"
"Enable suggestions" and move the slider for the suggestion threshold and cluster threshold
Select "Store name tags in photos"
Click OK.
Picasa will begin to scan your photos for faces. This process can take a while, but while it's running in the background you can start tagging them. Just follow these steps:
Add name tags in bulk or a few photos at a time.
In bulk: Click on the 'Unnamed People' album in the 'People' collection to see all unnamed faces from your photos in the one place. Faces are grouped by similarity, so adding a name will apply it to all the faces in that group.
Add name tags a few photos at a time:
Click the People button in the bottom-right corner when viewing any folder, album, or photo to see all the faces that appear in the selected photos. Add names to those that need it.
Create people albums. Keep tagging. Ignore the people you don't know.
Picasa will create an album for each person you tag in your 'People' collection. Over the thumbnail images of the People album, toggle the button to zoom in on faces or zoom back out to view the full photo.
You don't have to name everyone. Deleting an unnamed face or clicking the icon on a photo will place that photo in the 'Ignored' album. You can view the photos you've ignored at any time by clicking Show ignored faces at the top of the 'Unnamed People' album.
Confirm Picasa face suggestions.
Picasa uses the names you add to automatically add face suggestions to your albums. If you see an orange question mark next to a people album, go to the album and confirm these suggestions.
Click to keep the photo or to remove the photo from the album. If there are multiple suggestions, you can click Confirm all at the top of the album to mark all the suggestions as correct. Toggle
Click at the top to see just the suggested faces.
Don't worry if you make a mistake when adding name tags. If a face ends up in the wrong people album, select the photo and click the Remove button at the top (or press the Delete key on your keyboard) to send it back to the "Unnamed People" album.
Tips:
Add name tags manually: If Picasa misses a face in your photo, when viewing a photo click the "Show/Hide People Panel" button
There you can add a tag by clicking the "Add a person manually" button at the bottom of the panel.
Change profile photos: You can change the photo displayed next to each album in the People collection. Just right-click (Windows) or Control-click (Mac) the face you'd like to use and select Set as Album Thumbnail.
Choose which folders to scan for faces: Just click Tools > Folder Manager and toggle face detection on/off for any folder
Deleting name tags
If you don't want face tags in your Picasa photos, the following steps will remove all face tags and people. This method removes the face tags from both Picasa and the photo metadata.
How to remove all face tags and People Albums including Unnamed and Ignored:
Start Picasa and make sure it is done scanning for photos and folders. It may still be scanning for faces.
Go to the Tools menu > Options, then Name Tags tab and verify that:
"Enable face detection" is OFF (unchecked)
"Enable suggestions" is OFF (unchecked)
"Store name tags in photo" is ON (check marked)
Click OK if you made any changes.
Go to the Tools menu > Folder Manager and make sure face detection is ON for all folders you want to clean out. On the right side of the Folder Manager under "For the current folder" you'll see either "Face Detection On" and a green check mark, or "Face Detection Off" and a red circle with slash.
Go to the top level Folder (usually My Pictures) and check that Face Detection is on.
Make sure Face Detection is on for all of it's subfolders with photos.
Make sure Face Detection is on for any other folders being watched by Picasa that have photos with faces.
Click OK if you made any changes.
Go to the search bar at the top of Picasa and enter the string: -xyzzyz
This text finds any photos that do not have "xyzzyx" in their tags or data. In other words, this will find all your photos.
In the left panel, go to the "Albums" collection and scroll to the top.
Select the green album called "Search results for "-xyzzyz" (This displays all your photos)
Select all photos by left-clicking any photo thumbnail in the library then press Ctrl + A on the keyboard (hold the Ctrl key and press the A key)
Right-click on any photo and select "Reset Faces"
After faces are reset, click the green "Back to View All" button in the green bar at the top of the thumbnail library.
In the People collection, all people albums should now show (0) meaning no faces are tagged; and Unnamed and Ignored albums should also show 0). You will now delete every empty people album one by one.
Select the first face, then press the delete key (there will be no "are you sure" confirmation window).
OR - Right-click on each individual empty person album and select "Delete People Album"
Unnamed album: At the the very top of the People collection, you may see an album called Unnamed
Click the "Expand Groups" button (upper right corner)
Select all (Ctrl + A) then delete all the faces by pressing the delete key
The people names are still in your contacts and will be given as suggestions if you start naming faces again. See the next section below for how to remove contacts if you want to completely remove name tags from Picasa.
How to remove contacts from the Picasa database
If you don't want any of the names of the previously listed people to appear as suggestions if you later want to name faces again, either rename or delete the Contacts file in the Picasa database as follows.
Close Picasa before beginning with these directions.
Navigate to the Google application data folder on your computer. There are numerous ways to get there; below are 3 methods:
Open Windows File Explorer by pressing the Windows key and letter E.
Or - press the "Windows" button on your keyboard plus the R key to open the Run window
Or - click the Start button (lower left corner of your desktop), type Run, then hit the Enter key to open the Run window
Copy and paste the appropriate path below (depending on your operating system) into either the path field of File Explorer or into the Run window:
Windows XP: %userprofile%\Local Settings\Application Data\Google\Picasa2\Contacts\
Windows Vista / Windows 7 / Windows 8 / Windows 10: %LocalAppData%\Google\Picasa2\Contacts\
The Contacts folder will open and you will see a file named "contacts.xml"
You can either rename this file or delete it to remove the contacts from the Picasa People manager:
To rename: Click on the Contacts.xml file, press F2 and rename it to something like contactsOLD.xml
To delete: Click on the contacts.xml file and delete it (press the Delete key)
Close the Contacts folder, then start Picasa
In Picasa, go to the Tools menu > People Manager and verify that it is empty
After the face tags and People albums are removed, if you wish to start fresh, go to the Tools menu > Options, Name Tags tab and turn on (check mark) the "Enable face detection" and "Enable suggestions" boxes. Be sure that "Store name tags in photo" is also check-marked. Click OK. Picasa will restart scanning for faces.
Uploading to Picasa Web Albums (now obsolete)
Face tags could once be viewed at the currently retired Picasa Web Albums website. After May 1, 2016, Picasa Web Albums was archived at a website called Album Archive where you can view your face tags.
Uploading to Google Photos
Uploading to Google Photos no longer works using Picasa. You will need to upload using other methods. Unfortunately, name/face tags created using the Picasa desktop program will not transfer to Google Photos when you upload those photos. Google Photos has its own automatic face detection system that will group like faces and allow you to name them.
If you've stored your face tag info in the metadata of the picture using Picasa, the tag will not be lost. Another program (as long as it preserves your metadata) will keep the face tag info. HOWEVER, it may not display the face tag or let you search for it or change it. This is the case with Google Photos. Google Photos doesn't use, display, or search for existing face tags created using Picasa - it just ignores the tags even though they still reside in the metadata.
Face group information which is created in Google Photos is NOT copied into the metadata of the photo, so if you download a picture from Google Photos, the new face tag information will NOT be stored in the metadata. When you download the photo, you'll still have the old face tag info that you added with Picasa. More about Google Photos "face groups" and applying labels: Find people, things, & places in your photos
Adobe Lightroom also handles facial recognition and face tagging, but does it differently than Picasa. If you ever decide to migrate to Lightroom, there is some 3rd party donation-ware which will translate Picasa-style face tags to the form of face tags that Lightroom will work with.
Beginning around April 2017, people reported that their "People" albums at Google Photos suddenly were gone. Over the next several months, people reported that some faces were no longer being detected. If "Face grouping" is allowed in your country, double check that your face group settings are on:
Open Google Photos app
Click the gear icon (top right) which will open "Settings"
Click "Group similar faces"
Make sure "Face grouping" is toggled on
Click View and manage people
Tip: If you live in any country that doesn't allow face tagging, you can go to a country where it is allowed then sign into your Google account. Afterwards, you may see that face grouping is now available to use inside the banned country. You could also use a free VPN program such as TunnelBear to change your location and turn on face grouping.