How to get Rid of Duplicate Images on your Computer
How to Delete Duplicate Images
If you are only looking to find and remove images that are "exact" duplicates of each other, Google's Picasa desktop software could be a good solution. Just import all your picture folders into Picasa and then choose Tools -> Experimental -> Show Duplicate Files to see a list of potential duplicates.
While removing duplicate images with Picasa, please remember that the software will list all copies that are found of an image including the original one. You therefore need to keep one of these copies and delete the rest as demonstrated in the above screencast.
Alternatively, create a separate folder that's not included in Picasa and move all the potential duplicate photographs to that folder instead of deleting them.
Find and Delete Similar Images (not exactly duplicates)
Now Picasa is a good solution for deleting identical duplicates but your disk may also be storing have pictures that look similar visually but may differ as far as pixels or bytes are considered. Such files won't be recognized by Picasa as duplicates but VisiPic, a tiny utility for Windows, can come really handy here.
To get started, launch the program and click File -> Add Folder to add folder(s) that you want to scan for duplicates. Then slide the Filter to somewhere between "Strict" and "Basic" so that program may group images that are similar or only slightly different. Hit play to begin scanning for duplicates.
To eliminate the duplicates, just move your mouse over the thumbnails and left-click the pictures you want to delete. They'll be marked with a recycle bin icon and you may then either choose "Delete" or even "Move" to transfer them to a separate folder.
The tool is also smart enough to auto-select images for deletion that either have lower resolution or lower file-size than the original image.