<html>
<head>
<meta http-equiv=Content-Type content="text/html;charset=utf-8">
<script>
y=1;
function imgs()
{
var myImg=document.getElementsByTagName("img")[0];
myImg.src=y+".jpg";
if(y==2)y=1;
else y++;
}
</script>
</head>
<body onload="setInterval(imgs,1000);">
<div align="center">
<img src="1.jpg">
</div>
</body>
</html>