自动选择留言板

代码说明：

  这里有个简单的办法可以帮你自动选择留言板。我们知道，如果浏览器试图下载一个不存在或者说是来自错误地址的图像，服务器会返回给浏览器一个错误信息，然后由浏览器直观地告诉你当前地址的图像不存在，这就是html文档的图像载入错误事件(There is a simple way to help you to automatically choose the message board. We know that if the browser to download a non-existent or wrong addresses from the images, the server will return to the browser an error message, then by the browser to tell you directly addresses the current image does not exist, and this is html files contained images of the incident wrong)