<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
    <script>
        var work = $('body');

        var backgrounds = new Array(
            'url(img/contentbackground1.jpg)'
          , 'url(img/contentbackground2.jpg)'
          , 'url(img/contentbackground3.jpg)'
          , 'url(img/contentbackground4.jpg)'
        );

        var current = 0;

        function nextBackground(){
            current++;
            current = current % backgrounds.length;
            work.css('contentbackground1', backgrounds[current]);
        }
        setInterval(nextBackground, 1000);

        work.css('contentbackground1', backgrounds[0]);
    </script>