In Picasa, you can start the Show Duplicate Files tool by selecting the Tools  menu -> Experimental -> Show Duplicate Files menu choice.

(This gives you a Picasa report showing you all the photos Picasa thinks are duplicates).

 

 This report shows you all the folders that have a photo that is a duplicate and, under each folder, all of the photos in that folder that are duplicates. It also shows you any albums that references any of these duplicate photos. Photos actually exist only in folders.  Albums do not have their own copies of the photos.  Albums simply "refer to" or "point to" photos, which always live in folders

 

 Click here for more on Folders Vs. Albums. The fact that a photo appears in an album does not make that photo a duplicate.  To be a duplicate, the photo has to exist more than once in the folders. It's important to know about the albums, though, because if copies of same photo exist in two separate folders (and thus, are duplicates) and an album is referencing one of those duplicate photos, you want to be sure to delete the right copy of the duplicate photo from the right folder.  That is, you probably want to delete the photo that is NOT being referenced by the album.  That way, after the delete, the album still has a photo to reference.

1. Be sure you have a current backup of your pictures.
2. Check for and eliminate Phantom Duplicate Folders.
3. Run the Tools -> Experimental -> Show Duplicate Files tool to display all duplicates
4. Mark Duplicates that are in Albums so you will not accidently remove pictures that are linked to Albums.
5. Eliminate Duplicate Folders
6. Delete the duplicate copy of the pictures.
7. Clean up afterwards.

Do a Full backup of your Picasa Photos 

Before you begin any task in Picasa that could result in photos being deleted, it's always good to do a full backup. If you mess up and delete the wrong thing, you can restore it from the Backup. You can use the built-in Picasa Back Up Pictures tool or an external backup or copy / sync tool.

 

Picasa's built-in Backup tool is Ideal for this backup because it includes a restore function that restores only deleted files. It also saves the pictures in uncompressed format so you can selectively restore even a single picture.

 

Back up Pictures Using the  Picasa Backup tool:

1. Go to the Tools menu and select "Back Up Pictures".
2. In the Backup tool box 1 select New Set So you will create a new complete backup, not an Incremental backup.
    
   

    
3. In the New Backup Set box that comes up, Name the backup set and select Disk-to-disk backup.
4. You will need a hard disk or external hard disk with enough free space to contain your complete photo collection.
5. Select the Backup drive and folder to contain the backup set, and select all file types to be backed up.
6. Then click the Create button to create the new backup set.

    

   

    
7. In the Backup tool box 2, click "Select All", then click the "Burn" Button to create the backup set.

The backup set will be created in the drive and folder you named and will contain the PicasaRestore.exe program you can use to restore all missing photos to the Original locations.  You can also Explore the backup folder tree to find individual photos to copy back to the original location if you just want to restore a few deleted files.

Check for and Eliminate Phantom Duplicate Folders

Sometimes the Picasa Database can be messed up and show "Phantom Folders".

Phantom Folders are where the same Folder is shown more than once in the Picasa Folders collection. Phantom Folders will normally be shown next to each other in the left-hand column in Picasa under "Folders".

 

Configure Picasa Settings

1. Go to View menu -> Folder View, and set the folder view to Tree View. Also set Folder View to Sort by Date, or Sort by Name, whichever is easier for you to look through.
2. Set the folder window width to wide enough to see complete folder names by dragging the separator bar between the folders and the thumbnails to the right to make it wider.
3. Set the Column to the right of the thumbnails to the Properties screen by clicking on the blue circle with a "I" inside in the lower right.

Find Phantom Duplicate Folders

1. Look through the Folder names in the Folders collection on the left 
2. When you find 2 or more names that are exactly the same, Check to see if their Paths are exactly the same. If they are, both entries are the same folder which means one is a Phantom.
   Check Paths one of these 2 ways:

• Locate on disk method:
  Right-click on one of the folders and select Locate on Disk,
  Next, right-click on the second folder and select Locate on Disk.
  For each folder, a Windows Explorer window will open.
  Compare the Paths in the 2 WE address bars, and if they are both the same Windows folder, one is a phantom folder entry in Picasa.
• Folder Tool-Tip Method:
  Click on one of the folder names in the Folders collection.
  That Folder will be selected and it's name will be at the top of the thumbnails in the center column.
  In the center column, Hover the mouse pointer over the Manila Folder Icon to the left of the folder name.
  The complete folder path will appear in a yellow tool-tip box near the mouse pointer.
  Repeat the above with the second folder.
  If the paths in the tool-tips are identical, one of the folders is a Phantom.
   
  
   

Remove Phantom Duplicate Folders

1. Click on the folder name of one of the two identical folders above.
2. Go to the Tools menu -> Folder Manager, and the folder name should be highlighted in the folder tree on the left in the Folder manager.
3.  Click on the Remove from Picasa (Red X) button on the right, then select OK to exit the folder manager.
4. Both Folder names will probably be removed from the Folder Collection.
5. If both names are gone, go back into the Folder Manager and set the Folder (which now should have  red X to "Scan Always" (blue circular arrow)
6. Picasa should re-scan the folder and only the single folder name should appear.

Note: 
If both folder names were not removed in step 3 above, click on the second Folder Name and go to the Folder Manager again.
If the second name does not point at the (Red X) folder you removed in 3 Above, it is not a Phantom duplicate, and is a real duplicate of the first folder in a different Path.  Treat it as a real second copy of the folder.  Make sure you remember to set the first folder back to Scan Always.
 

 
 

Ensure that no Backups or other Unwanted Folders are being Watched by Picasa

Backups of Folders will contain copies of photos, but they are duplicates you want to keep so you can restore your photos if necessary.

You could also have folders that are not being watched by Picasa and of course Picasa cannot detect duplicates unless the Folder is being Watched.

1.  Go to the Tools menu -> Folder Manager, and notice the Drive and Folder Tree on the Left, and the Watched Folders list in the lower right..
2.  In the Watched Folders list make sure no drives or folders containing Backups are being Watched.
   If you find something being watched that you don't want to be watched by Picasa, Click on the Watched Folder and press the Remove from Picasa button.
3. In the Drive and Folder tree on the left, drill down through the folders and subfolders and make sure all folders you want to see (Watch) in Picasa are set to Scan Always, and that all Drives and Folders you don't want to see (Watch) in Picasa are set to Remove From Picasa. It is usually a bad idea to Watch a whole drive, because there may be incidental Photos or graphics used for other purposes that you wouldn't want to clutter up your photo collection. 
4. In the Drive and Folder tree on the left, drill down through the folders and subfolders and make sure no Drives or Folders are set to Scan Once (Green Check-Mark). Normally nothing will be set to Scan Once. If you find something, set it to Scan Always, or Remove From Picasa depending on if you want to see it in Picasa or not.

Mark Duplicates that are Referenced in Albums 

Note: If you don't use Picasa "blue" Albums or don't care if some duplicated photos may be removed from the Albums you can skip this topic.

 Albums do not contain Pictures themselves, they just contain pointers to photos that exist in Folders. The fact that a photo appears in an album does not make that photo a duplicate.  To be a duplicate, the photo has to exist more than once in the folders. It's important to know about the albums, though, because if copies of the same photos exist in two separate folders (and thus, are duplicates) and an album is referencing one of those duplicate photos, you want to be sure to delete the right copy of the duplicate photo from the right folder.  That is, you probably want to delete the photo that is NOT being referenced by the album.  That way, after the delete, the album still has a photo to reference 

Configure Picasa Settings

1. Start the Show Duplicate Files tool:
   Go to the Tools menu -> Experimental -> Show Duplicate Files.
   All  "Blue" Albums that reference photos that are duplicates will be shown in the Albums collection.

Mark Duplicate Photos that are referenced in Albums

Note: This Procedure uses the Star Icon to mark the duplicate photos referenced in Albums so you can avoid deleting those Photos. If you use the Star Icon for other purposes, just be aware that the duplicates in Albums will also be marked with a Star.

1. In the Albums Collection, click on the first album..
2. Go to the Edit menu -> Select All (or type Ctrl+A on the keyboard) to select all the duplicate photos in that Album.
3. Just above the Green Share button is a white Star outline. Click it to make it Gold. This will set all the duplicate photos to Starred and put a small gold star in the lower right corner.
    
4. Repeat the above steps in each Album so all Duplicates that are in Albums will be starred.

After this procedure, all duplicate photos that are in Albums will be marked with a Star.

In the Eliminate Duplicate Folders, and Delete Duplicate Photos procedures below you should give preference to any photos with a gold star as they may be referenced in Albums, and deleting them will remove them from the Album.

 

Eliminate Duplicate Folders

A common cause of Duplicate Pictures is Duplicate Folders.

Often when people are collecting or arranging photos, the same set of photos will be placed in more than one Folder. 

In this topic we discuss how to eliminate duplicate folders without losing unique photos that may be in one but not the other

 

Configure Picasa Settings

1. Go to View menu -> Folder View, and set the folder view to Tree View. Also set Folder View to Sort by Name.
   Tree View is required when Deleting Folders because when you delete a folder, all subfolders are also deleted, and in Flat File View there is no indication that a folder contains subfolders.
2. Set the folder window width to wide enough to see complete folder names by dragging the separator bar between the folders and the thumbnails to the right to make it wider.
3. Set the Column to the right of the thumbnails to the Properties screen by clicking on the blue circle with a "I" inside in the lower right.
4. Start the Show Duplicate Files tool:
   Go to the Tools menu -> Experimental -> Show Duplicate Files.
   All Folders will be shown that contain Duplicate photos.

Find Duplicate Folders and Combine or Delete Them

1. Look through the Folder names in the Folders collection on the left  To the right of the name is the number of duplicates in that folder.
2. When you find 2 folders that contain the same number of photos it is likely that they are duplicates of each other.
3. To see if they are duplicates of each other, right-click on each of the folders and select Sort Folder By... -> Name.
4. Compare the 2 folder's duplicated contents and decide which folder you want to keep.
5. In the folder you want to delete, Select the last photo and do File menu Save a Copy.
   This makes sure there is at least one photo in the folder so we can find the folder in Picasa later.
6. Select all the duplicates in the folder that is to be eliminated, then press the Delete key to delete them.
   Note: If you have Starred photos that are in Albums, don't delete the Starred photos.
7. In the Green bar at the top of the thumbnails, click the green button Back to View All to see all remaining files in the folder to be eliminated.
8. In the Folders, find and click on the folder to be eliminated.
9. Move all the photos in that folder, EXCEPT for the copy you saved above,  to the Folder you are keeping.
   Note:  Starred Photos will be renamed with a -001 after the file name, but will stay in the Albums.
10.  When the folder to be eliminated is empty except for the copied photo, right-click on the folder and select Delete from Disk. The folder to be eliminated is now deleted.
11. Start the Show Duplicate Files tools again and repeat steps 1 thru 10 for each duplicate Folder pair.

 

Delete Duplicate Photo Files

Compare and Delete Duplicate Photos Side-by-side

1. With Show Duplicates tool still active, Go to the Albums collection and click on the search results green Album..
   The duplicate photos will now be listed side by side.
2. If you wish you can drag the separator bar between the folders column and the thumbnails to the right until only 2 photos are shown.
3. The duplicates should be side by side, but may get out of order if there are an odd number of duplicates.
   Even if out of order, one duplicate will be to the right and one will be left when only 2 columns of photos are shown.
4. You can click on any photo and the Properties panel on the right will list the name, size, location etc. of that photo.
5. Drag a selection box down the right column of duplicates to select around 50 of them.
6. Any photos that have a Gold Star in the lower right may be referenced in an album, so scroll down the selected column and Ctrl-Click any photos with a star to deselect them from the selection. 
7. When you are satisfied that the selected duplicates can be deleted, Right-Click on a selected photo and  Delete from Disk (or push the Delete key on the keyboard). .
8. The Photos selected will be deleted, and the other half of the duplicate set will be removed from the duplicate list.
9. The total number of duplicates is listed in the green bar at the top of the thumbnails.
   This total number should go down by approximately twice the number of photos deleted since the other half of the duplicate set will also be removed from the list as it is no longer duplicated.  The number will not be exactly twice the number of deletes if there are more than 2 copies of the same photo.
10. Repeat the above steps for each folder in the Folders collection. Don't delete so many duplicates at a time that you lose track.

 

1. When all you have left are a few starred photos and their paired duplicate that were not deleted because they were in the wrong folder, select the unstarred photo of the pair, push the F2 key, and rename it by adding Dup- to the start of the file name.
2. Go to the Folders collection and drag the starred photo from it's present Folder to the folder with the duplicate if you would rather have it there, or wherever you wish, then delete the file with Dup- prefix.
3. If you marked albums with stars you should go back and un-star the album photos.
    - In the Albums Collection, click on the first album..
    - Go to the Edit menu -> Select All (or type Ctrl+A on the keyboard) to select all the duplicate photos in that Album.
   -  Just above the Green Share button is a  Gold Star outline. Click it to make it White. This will clear the star on all the duplicate photos.
   - Repeat for the rest of the Albums
4. In the Green bar at the top of the thumbnails, click the green button Back to View All to see all photos and folder again.