var xPos = 1576;
var right = 1;
var speed = 45;

$(function(){
	setInterval ( move_bg, speed );
});

function move_bg(){
	$("#foto").css({backgroundPosition: xPos+'px 0px'});
	if(right == 1)
		{
		xPos--;
		if (xPos == 900) { right = 0; }
		}
	else
		{
		xPos++;
		if (xPos == 1576) { right = 1; }
		}

	}