如何判断图片地址是否失效

  <html>

  <body>

  <IMG src="http://www.google.com/logos/Logo_25wht.gif" alt="图片来源正常"></p>

  <IMG src="abc.gif">

  </body>

  </html>

  <script language="javascript">

  var AllImages=document.getElementsByTagName("IMG");

  for(i=0;i<AllImages.length;i++)

  {

  var img=AllImages[i];

  img.onerror=function()

  {

  this.src="http://www.yaosansi.com/blog/logo.gif";

  this.alt="图片来源错误";

  }

  }

  </script>