there are some criteria that can be used: - photo is clearly visible, not dark, not overburned, etc - composition is ok, no cut-off's, there is space around the main object(s) - any other common-sense criteria for visual appealing image (?)
it's hard to come up with something like that since it could be part of the idea (to overburn the photo or to decompose a composition). I'd say quality of the idea is much more important than photo-skills.
Another explanation could be that a player just sucks and despite planning and importance he shows poor results. A better criteria should be defined e.g. "was a player capable in the past and quality went down recently?" That would be a better sign of lost interest.
but not always. I can think of case when too great photo posted can discourage others from participation. Take recent example when Tanaha said "I won't post, since my ideas are worse than ones already posted"