We are constantly working on our core algorithms to ensure ImageDuels and the site in general are fun. Repetition of image pairings is definitely something we are conscious of and are working to resolve. We have made great strides already as it used to happen much more frequently.
I am in agreement with you as I don't think a user should see the same two images paired together in the same session. That said, it is possible right now.
We'll keep working on it! Please keep the feedback coming. Thanks!
there has to be a problem with the seeding of random numbers in your algorithm. I've gotten the SAME SEQUENCE of images more often than not. It starts fine, but I usually get the same sequence later. It's as if you're somehow using the same seed after a certain number of image duels.