[TAG] JPEG de-duplication

[Neil Youngman]

A family member has a number of directories containing photos in JPEG format. 
3 directories contain different versions of the same collection of photos. 
One is the current master and the others are earlier snapshots of the same 
collection. I believe that all the photos in the older snapshots are present 
in the current master, but I would like to verify that before I delete them. 
Also many other directories probably contain duplicates of photos in the 
master collection and I would like to clean those up.

Identifying and cleaning up byte for byte identical JPEGs in the snapshots has 
freed up a considerable amount of disk space. A sample of the remaining 
photos suggests that they are probably in the master, but the tags and 
position in the directory tree have changed. I don't want to go through 
comparing them all by hand. 

Initial research suggests that ImageMagick can produce a "signature", which is 
a SHA256 checksum of the image data. I believe that this would be suitable 
for identifying identical images, on which the tags have been altered. 

Are there any graphics experts in the gang who can confirm this? Alternatively 
suggestions of existing tools that will do the job, or better approaches, 
would be most welcome.

Neil