Allow users to only vote once in form?

They can only vote for 1 photo and they leave their name and email with the vote (so they cannot vote twice).

If you wish to limit your users to vote per unique email. That is possible by enabling your form limits.

Here's a guide about it: 

To limit submission per unique answer in your form fields (like your email field), then you can follow this guide: http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question 

To limit your submission per browser OR by unique IP, you can follow this one: http://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form 

 

I hope that helps.