AJAX :: Image Is Visible In Image Control In Design Time But Not Visible On Runtime

I am learning asp.net using Visual web developer 2008 express.

I have an image control with the html code below

<div class="Header">
<asp:Image ID="image1" runat="server"
ImageUrl="D:/Master/test.jpg" Width="500" Height="300"
AlternateText="UNRA Fort Portal Intranet"/>
</div>

In design view, the image shows but when i run the app, the image is not shown. Only the alternate text is displayed.

 The css code code as  below.

.Header
{
top:10px;
left:20px;
position:absolute;
width:800px;
background-image:URL(D:/Master/test.jpg);
background-repeat:repeat-x;
}