From http://www.w3schools.com (Copyright Refsnes Data)

.NET Mobile Images

.NET Mobile displays different types of images for different types of devices.

The Image Control

Different mobile devices have different display capabilities.

The Image Control allows the developer to specify different types of images for different types of devices.

Image Types

Some mobile devices will display GIF images. Other mobile devices will display BMP images or WBMP images. The Image Control allows you to specify different images for each preferred image type.

This mobile page displays an image:

<%@ Page
Inherits=
"System.Web.UI.MobileControls.MobilePage"%>
<%@ Register
TagPrefix="Mobile"
Namespace="System.Web.UI.MobileControls"
Assembly="System.Web.Mobile" %>

<Mobile:Form runat="server">
<Mobile:Image runat="server">
  <DeviceSpecific>
    <Choice ImageURL="image.gif" />
    <Choice ImageURL="image.bmp" />
    <Choice ImageURL="image.wbmp" />
  </DeviceSpecific>
</Mobile:Image>
</Mobile:Form>

When this page is displayed on pocket PC, a GIF image will be displayed. On a cell phone a WBMP image or a BMP image will be displayed, according to the characteristics of the cell phone.