Taking photo of other's sculpture can be prevented by asking for two photos in different stages of making the sculpture.
But you have a point considering second paragraph of your comment. If you are going for artists that will communicate with the audience this is actually a great concept. Taking that in regard my previous remarks are meaningless :)
@tripdespider yes but you can also download pictures from another artist diary with stages of sculpture (there is many online and people are known to claim other people's work)
I am glad you understand the concept and hope I will see you enter the contest in the future