I always thought it was meant to post on the last day haha I just wait for your "last day" warning so I can write my post.
You should figure out a way to use your "real" participants, those you trust to help on the task to find plagiarism by pointing to you the photos that are not original/are copy/or came directly from google. That way it's a little less work for you and more fun for us.
I agree with you and that is something I am working on
Even I got to know yesterday itself that the contest was open throughout the week 😂 I would check @juliank profile to see that last day post so that I could publish my blog