function generar_imagen(){
	var num;
	num = Math.round(Math.random()*5) + 1;
	if(document.getElementById("imagen_aleatoria")){
		document.getElementById("imagen_aleatoria").innerHTML ='<img src="/img/cabeceras/imagen' + num + '.jpg" alt="NorteSport" title="NorteSport" width="800" height="199">'
	}
}