How select a blank image when i am not upload a file

I think if client does not want to upload an Image then you should return some proper message. But any way if you want to send an empty image then just create a file 1.jpg in specified folder and upload it. You can use below given code for creating dummy image file

using (System.IO.FileStream fs = System.IO.File.Create("c:\\dummy.jpg"))
{
    fs.Close();
}