Good tool for finding photo duplicates based on image data [closed]

What is a good (and preferably free) tool for finding photo duplicates based on the photos themselves?

So, not filename, filesize etc., but how the photos look like. It would be nice if it managed to match photos that were the same image, but not exactly the same size for example too.

Solution 1:

SimilarImages is a free application designed to find similar images (duplicates) on your hard drives.

Description:

This simple GUI will help you to easy check your images for duplicates It includes the following Preferences:

• Configurable Threshold: You may change the threshold depending on your needs. Once analyzed you may change the threshold without having to analyzed images again (if you don't alter the list)
• Three search types:
  • Normal Search - which will compare all images with all other images
  • Inclusive Search - which will only compare images contained in same folder with each other
  • Exclusive Search - which will only compare images not contained in same folder
• Semi-Automatic-Deletion: You may choose a rule which will preselect a file in review mode, so that you don't have to compare all the file properties yourself. Furthermore you may use the Auto-delete 0-Files feature which will apply the rule on all image pairs which are most similar.
• Result Cache that will seamlessly cache all the generated data so that later searches for already analyzed files will be much faster.
• Not-A-Match Database that will remember all non-matches.

Solution 2:

GQView is free and can find duplicate images by similarity:

There is a Windows port, though I've only used it in Linux.