Ideally, the best cosplay photography contests would have a panel or seasoned and well-respected cosplay photographers judging it. The panelists themselves can be regulars in the con world like me and emerging talents.
The metrics of how it is judged is difficult, since technical qualities should count, but should the cosplay posing and crasftmanship be also judged? If they are, what weight will it carry? Should post-processing be allowed and what is considered acceptable/unacceptable?
This sort of debate would be interesting, but for them to even start the debate it needs to be a serious contest.