If people are stealing my pictures, can i sue them?

What you have is not not a criminal issue, but a civil issue. You cannot steal what has been posted freely on the internet in the terms of a criminal court. Indentity theft requires that they steal personally identifying information to pose as you for the purpose of fraud. If they simply take a picture and tell everyone visiting the site that they are you, there is no crime. You can however consult an attorney that specializes in intellectual property cases and see if they believe you have a case.