The primary domain of this competition is a field of computer vision called copy detection.
Arguably, copy detection has not received as much attention as other fields of computer vision like object classification or instance detection, but that's not because it's an easy problem. Our competition sponsors at Facebook AI regard copy detection as a problem without a clear "state of the art" and which remains unsolved, particularly at the scale required to moderate the huge volume of content generated on social media today.
The problem is made more challenging by the fact that it can be "adversarial" -- that is, efforts to detect and flag bad content will often elicit new attempts by users to sneak past the detection system the next time around.
For more background, you should definitely check out this paper that FB AI and their research partners have produced as it has a very thorough description of the problem space, competition and dataset.