If I copyright a photograph I put on the internet, does that mean other websites can't use it legally?

First, it is noted that copyright attaches to a work upon creation of the work, and registration is only necessary to enforce your rights in court.  Had you registered your copyright within 90 of the May 2012 publication of the photos on the website, you could have been entitled to attorneys fees and statutory damages. However, since you evidently did not, you would have to prove actual damage to collect money, but could obtain an injunction against use of the photographs. The copyright would cover not only use on another website, but also printing out of copies of the pictures. You could send notices to the various website owners advising them that they are violating your copyright in the photographs and demanding that they be removed, but if they do not do it voluntarilly, you could contact whatever service is hosting the website if it is not hosted by the website owner advising them of the violations and asking them to shut down the website untill the pictures are removed and your last option would be to institutle litiagtion, which could be costly.