There's something wrong with your trust score aswell your site seems offering a Ponzi scheme maybe you should fix those allegation first before having this contest and also after you done with this hand those reward money in the hand of escrow since good designers will not waste their time for creating an artwork for not secured rewards.
But honestly I don't like what I see in your site.
Exactly. Since it's already shown, I think the majority designers of the forum are wise enough of not joining this kind of contest because it's already figured out that the logo that will be made is for a ponzi.
to be honest i don't know why this picture worth more than 24 ETH.
I have gone through their website and this picture is likely you can search all over google and possibly grabbed it, compiled and edit to merge. The highest bid is 8.747 ETH and it's possible that they're the one that placed it to make others bid more.