As sibling comment mentions, with OCR and video tooling these days I'd imagine you could whip up something pretty easily that can comb through several minutes of video footage and convert it to text/PDF/etc.

A leaker with a smartphone on a tripod capturing video while they scroll through files etc. could probably deal significant damage without much effort.

Yeah, this is why any high security information facility has physical security controls. Give someone infinite time and physical access and they could copy it off with clay tablets and chisels.