I had experience about art contest when the winner is determined by public voting regardless it's a combination of judges + public voting, public voting alone etc. I can say it's not a good decision because the winner in this contest would be the most popular member, not the best art. I understand you might think public voting would be fair because it's transparent, but the reality isn't.

Having this rule will discourage few or even many artists to enter this contest.

I know the phrases "your money your rule", but this is just my comment.