Some background:Based on DjangoUser submitted contentI'm in the USA (NYC to be exact)Any other relevant information you need to make a suggestion, just ask in comments.
Is adding all rights reserved or copyright in the bottom of my webapp necessary? And why?
copyright
From Related questionYou automatically have the copyright  to any work you create. There isn't an  official register of copyright. You  can apply for trademarks and patents  if you have anything that qualifies.Based on that answer I'd say it is unnecessary for your own content. As for the user submitted content it gets sticky. What if someone has posted copyrighted content of their own or from another source? You cannot claim copyright on it yourself as it has already been copyrighted by someone else. If you want to copyright the original content of user submitted content you will need to make sure your terms of service state that any original content posted by your users is copyright by you and make sure they have to agree to those terms before submitting content so they cannot claim ignorance if you do use their content for your own purposes. 