I have a suggestion - change it from self-portrait to something else. Because when I saw the contest, I honestly could not think of how to create one and after creating two, I am really out of ideas for third one.

People would participate only if they would be able to figure out on what to do here. Self-portrait is tough. Maybe lets make it a selfie contests. Selfies are great and you can give people theme like - Smiling selfie, angry selfie, selfie with tree, selfie with sky.

Maybe.
Since you are working so hard for this, I would love it to get popular.