How do I reference the directory were the images are now stored on the server via the webconfig "key" with DataList Control?

I am currently storing 50+ images in Web Application folder:
~/ProductImages/.....jpg
I am displaying these images with a DataList control and it works just fine, html code below:
<asp:DataList ID="list" Runat="server" RepeatColumns="2" EnableViewState="False" OnItemCommand="list_ItemCommand">
  <ItemTemplate>
    <table cellPadding="0" align="left">
      <tr height="105">
        <td align="center" width="110">
          <a href='Product.aspx?ProductID=<%# Eval("ProductID")%>'>
            <img alt="Product Image" width="100" src='ProductImages/<%# Eval("Image1FileName") %>' border="0"/>
          </a>
       ...