HtmlInputFile 
HtmlInputImage
Allows programmatic access to the HTML <input type=hidden> element on the server.
The HtmlInputHidden control <input type=hidden runat="server"> is used to create a control that is not rendered but whose value is submitted with a form.
The hidden input type presents no control to the user. It simply provides a mechanism for storing and delivering information to the receiving program without user interaction.
This technique is commonly used to persist session-dependent information without using cookies or session state. The Web Forms framework uses this feature of HTML to automatically store and restore the view state of ASP.NET server controls across round trips to the server.
The following sample illustrates using the HtmlInputHidden control.
HtmlInputHidden Control Syntax HiddenField Web Server Control HTML INPUT Element