Check file exists using url

How to check file exists using url, normally we have to use file exists controller on server like
File.Exists()  its working but url path like http://localhost:8081/assets/photos/test.jpg is not working. Please anyone explain ASAP

var url = "http://www.domain.com/image.png";
HttpWebResponse response = null;
var request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "HEAD";


try
{
    response = (HttpWebResponse)request.GetResponse();
}
catch (WebException ex)
{
    /* A WebException will be thrown if the status of the response is not `200 OK` */
}
finally
{
    // Don't forget to close your response.
    if (response != null)
    {
        response.Close();
    }
}