To get percentage of similarity of two images use the following request with parameters:
src url to a first image
dst url to a second image
for example: http://qr.unsode.com/imagecomparer.aspx?src=http%3a%2f%2fqr.unsode.com%2fimage1.jpg&dst=http%3a%2f%2fqr.unsode.com%2fimage2.jpg
Also, you may pass these parameters as GET/POST parameters

In response you will get the "similarity-percentage" Http Header with the percentage of similarity, as well as http response body with the same decimal percentage value.

Send Bitcoins to: 1vqHSTrq1GEoEF7QsL8dhmJfRMDVxhv2y