function alteraBackgroundImage() {
	largura = window.screen.width;
	
	if(largura == 800){
		document.getElementById('body').style.backgroundImage = "url('../img/fundo800.jpg')";
	}
	if(largura == 1024){
		document.getElementById('body').style.backgroundImage = "url('../img/fundo1024.jpg')";
	}
	if(largura == 1280){
		document.getElementById('body').style.backgroundImage = "url('../img/fundo1280.jpg')";
	}
}