写入MYSQL数据库数据为空，不知何解？

Sub aa()
Dim MyStream As New IO.MemoryStream
PictureBox1.Image.Save(MyStream, System.Drawing.Imaging.ImageFormat.Bmp)
'Dim MyBytes(MyStream.Length) As Byte '声明数组
Dim MyBytes
MyBytes = MyStream.GetBuffer

Dim mCommand As MySqlCommand = New MySqlCommand()
Try
If Cn.State = ConnectionState.Closed Then
Cn.Open()
Dim mSQLcomm As MySqlCommand = New MySqlCommand("set names gbk", Cn)
mSQLcomm.ExecuteNonQuery()
mSQLcomm.Dispose()
End If

mCommand.Parameters.Add(New MySqlParameter("img", MyBytes))
mCommand.Parameters.Add(New MySqlParameter("qq", "qqqq"))
mCommand.Connection = Cn
mCommand.CommandText = "insert into testx (img,qq) values (img,qq)"
mCommand.CommandType = CommandType.Text
mCommand.ExecuteNonQuery()
Cn.Close()
Catch ex As Exception
If Cn.State = ConnectionState.Open Then
Cn.Close()
End If
End Try
End Sub

以上代码可以正常运行，如果将insert into testx (img,qq) values (img,qq)改为insert into testx (img,qq) values ('img','qq')，两个字段能正常写入img和qq两个字符，但使用上述的方式写入时就显示为空，不知何解？请指教！