It would help if the authors explained how exactly they used the Elo rating system to evaluate quality, since this seems like a non-standard and rather unusual

It would help if the authors explained how exactly they used the Elo rating system to evaluate quality, since this seems like a non-standard and rather unusual use case for this. I am guessing that if an image is rated better than another that counts as a "win"? Finally, writing "ELO" instead of "Elo" is incorrect (this is just one of my pet peeves but indulge me nevertheless). This is some guy's name not an abbreviation, nor a prog rock band from the 70's! You would not write "ELO's" rating system for the same reason you wouldn't write "DIJKSTRA's" algorithm.