Try this
byte[] imagebyt = new byte[Image1.ImageUrl.FileBytes.Length+1];
imagebyt = Image1.Imageurl.FileBytes;
MemoryStream ms = new MemoryStream(imagebyt,0,imagebyt.Length);
cmd = new MySqlCommand("Insert Into db_image (Image) values (@imag)", con);
cmd.Parameters.AddWithValue("imag", ms.GetBuffer());
cmd.ExecuteNonQuery();
Your problem was that you set the length of the byte array but didnt actually tell them to put your image bytes there