nowTime=(new Date()).getHours();
if(nowTime>=0 && nowTime<7) {
  myImg="img/now-morning.jpg"; 
    } else if(nowTime>=7 && nowTime<12) {
  myImg="img/now-afternoon.jpg";
    } else if(nowTime>=12 && nowTime<14) {
  myImg="img/now-sunset.jpg";
    }else if(nowTime<14 || nowTime>=0) {
  myImg="img/now-night.jpg";
}
document.write("<img src='"+myImg+"'>");