How Do I Get Ride To Select Image Each Time When Record Is Updated

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C#5.0

i have a form in which i can save data about employee including image.image is saving/retrieve properly ,problem is that when i retrieve image is time then save or update the record without selecting image ,image is not going to save. i am using following code to save image

Employee.ImgBody = (Employee.ImgBody == null) ? new byte[0] : Employee.ImgBody;
               //Image saving code
               Byte[] imgByte = null;
               if (txtEpPicture.HasFile && txtEpPicture.PostedFile != null)
               {
                   //To create a PostedFile
                   HttpPostedFile File = txtEpPicture.PostedFile;
                   //Create byte Array with file len
                   imgByte = new Byte[File.ContentLength];
                   //force the control to load data in array
                   File.InputStream.Read(imgByte, 0, File.ContentLength);
                   Employee.ImgBody = imgByte;
               }

and retriving image by

empPicture.ImageUrl = string.Format("EmpPicture.ashx?id={0}", emp.Id);