var how_many_postcards = 13;
var now = new Date()
var sec = now.getSeconds()
var pc = sec % how_many_postcards;
pc +=1;

if (pc==1) {

postcard="images/postcard01.jpg";
width="149";
height="114";
}
if (pc==2) {

postcard="images/postcard02.jpg";
width="149";
height="114";
}
if (pc==3) {

postcard="images/postcard03.jpg";
width="149";
height="114";
}
if (pc==4) {

postcard="images/postcard04.jpg";
width="149";
height="114";
}
if (pc==5) {

postcard="images/postcard05.jpg";
width="149";
height="114";
}
if (pc==6) {

postcard="images/postcard06.jpg";
width="149";
height="114";
}
if (pc==7) {

postcard="images/postcard07.jpg";
width="149";
height="114";
}
if (pc==8) {

postcard="images/postcard08.jpg";
width="149";
height="114";
}
if (pc==9) {

postcard="images/postcard09.jpg";
width="149";
height="114";
}
if (pc==10) {

postcard="images/postcard10.jpg";
width="149";
height="114";
}
if (pc==11) {

postcard="images/postcard11.jpg";
width="149";
height="114";
}
if (pc==12) {

postcard="images/postcard12.jpg";
width="149";
height="114";
}
if (pc==13) {

postcard="images/postcard13.jpg";
width="149";
height="114";
}

document.write('<img src=\"' + postcard + '\" width=')
document.write(width + ' height=' + height + ' ');