Dhash

Dhash's (or difference hashes) are a way of calculating similarity between images. If two images have a similar dhash, then the likelihood is that they both are depicting the same image (albeit slightly cropped compressed etc).

For more information, check out the links below.

• http://hackerlabs.org/blog/2012/07/30/organizing-photos-with-duplicate-and-similarity-checking/
• http://www.hackerfactor.com/blog/?/archives/529-Kind-of-Like-That.html
• http://www.hackerfactor.com/blog/index.php?/archives/432-Looks-Like-It.html
• http://blog.iconfinder.com/detecting-duplicate-images-using-python/

gem 'dhash'

hash1 = Dhash.calculate('face-high.jpg')
hash2 = Dhash.calculate('face-low.jpg')

if Dhash.hamming(hash1, hash2) < 10
  puts "Images are very similar"
else
  puts "No match"
end