Bad design. Anybody could mess up the job. In any large, anonymous group, there will be a certain number of assholes. Of course it didn't work. Ask anyone involved in running an IRC channel, or a MMORPG, or a factory.

Given the problem they were solving (reassembling images shredded into strips) they needed something where, when two strips were put together by a human, a program decided if they matched closely, and, if so, locked them together for further editing. That would constrain the workers to make forward progress. You might need an unlock capability if there was a false match, but that should take the cooperation of several people.