<asp:Button ID="Button" runat="server" Text="popup"/>

<ajaxToolkit:ModalPopupExtender ID="pop" runat="server" TargetControlID="Button" BehaviorID="popupbehaviour"

PopupControlID="Panel1" CancelControlID="btnCancel" Enabled="True" />

<asp:Panel ID="Panel1" runat="server" Height="50px" Width="517px" BorderColor="blue"

BorderWidth="10px">

You are about to redirect to some other page are you sure want to do&nbsp; it?<br />

<asp:Button ID="btnCancel" runat="server" Text="Cancel" />

<asp:Button ID="Button5" runat="server" OnClick="Button5_Click" Text="OK" />

<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox></asp:Panel>

u can put any thing in the panel like images in ur case u want to show.

hope this helps