Make sure you have selected "Original Image Size" (see attached), add your class (see attached). Now id you are setting in CSS width 100% the image will only fill the width of it's parent container <div>. So you will need to sets its parent container to be 100% as well or it will never fill the whole page/screen. If you have code examples you can attach I can be of more assistance.
These are the opening divs before the picture (the Content place holder is where the pic is going) <div class="content-wrapper"> <div class="topPic"> <asp:ContentPlaceHolder ID="topPicHolder" runat="server"/> Now the classes: .content-wrapper margin: 0 auto; width:100%; height: auto; min-height:100%; .topPic clear: both; width: 100%; height: auto; text-decoration: none; .dunne width:100%; position:absolute; z-index:-5000;