I was trying to order my camera images when I found that I have already copied, resized, renamed many of them previously and now I can’t find a way to get rid of duplicates. What I needed was a tool to find visually similar images. After searching a while I found findimagedupes which is available in synaptic. A dry run showed promising results and soon I found it can also detect similar images with different aspect ratios, more than 2 similar images etc. Performance is quite good considering I ran it on a directory having around 7000 files in it. Now going through the output list to delete the extra copies.
$ findimagedupes Pictures/ > dups //get the output in dups file
To install on Ubuntu:
$ sudo apt-get install findimagedupes