<asp:GridView ID="GridViewImmagini" runat="server" AutoGenerateColumns="false" DataSourceID="AccessDataSource1">
   <Columns>
   <asp:BoundField HeaderText="Descrizione" DataField="testo" />    
<asp:ImageField HeaderText="Miniatura immagine" DataImageUrlField="mini_url"  
   DataImageUrlFormatString="images/{0}">      
</asp:ImageField> 
   </Columns>
    </asp:GridView>