its about the libpuzzle libray for php ( http://libpuzzle.pureftpd.org/project/libpuzzle ) from Mr. Frank Denis. I´am trying to understand how to index and store the data in
I've made a libpuzzle DEMO project on GitHub: https://github.com/alsotang/libpuzzle_demo.
The project use the way which Jason proposed above.
The database schema shows on: https://github.com/alsotang/libpuzzle_demo/blob/master/schema.sql
And I will give more information about libpuzzle's signature.

Now we have the two images, and let me calculate their signature.

The odd lines is for image 1(the left one), and the even lines is for image 2.
You can find that in most cases, the number in the same position is the same.
....
My english is so poor, so I cant express my mind continue...I think anyone who wanna index millions of images should inspect my GitHub repo of libpuzzle DEMO ..