Create an interactive spot the difference app for website and Facebook

I want an app built for my food-related Facebook page (My Easy Suppers), that I can also link from my website. I have thought of an interactive spot the difference photo competition (like on www.spotthedifference.com. I want it to capture visitors' emails, and, when completed correctly, to send visitors to another URL where they enter a prize draw. I will want to be able to upload the photos. Do you have any other ideas for other apps which enable me to capture email addresses? BTW, I don't have a big budget!