function mychange(){
hour=new Date();
myhour=hour.getHours();
if (7<=myhour&&myhour<15){document.write("<img src='images/photo_t01.jpg'>");
}
else if (15<=myhour&&myhour<19){document.write("<img src='images/photo_t02.jpg'>");
}
else {
document.write("<img src='images/photo_t03.jpg'>");
}
}