<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
</head>
<body style="text-align:center">
<img src="images/small.jpg" name="myImage" width="1002" height="754" id="myImage"/>
<script language="JavaScript" type="text/javascript">
var img = new Image();
img.src = "images/mm.jpg";
img.onload = function() {
document.getElementById(‘myImage‘).src = this.src;
}
</script>
</div>
</body>
</html>
原文：http://www.cnblogs.com/mrt-yyy/p/4449768.html