Forms Data Controls :: Display A Standard Picture On The GridView Field

I do have the following code for for a GridViewd that display pictures that are stored in a file. I am using AutoNumber(GUID) from the database to name the pictures before I stored them to the file. I can save up to 4 pictures using the same AutoNumber but adding these ending to it, Pic1, Pic2, Pic3 ,,,,etc.

The problem that I am having is that after I get the AutoNumber from the database, I want to display a standard picture on the GridView field if there is not particular picture associiated to this record in file. The name of the standard picture is located in the same file under the name of NoPicture.gif. How can I do this? So far this is my GridView code and it is working fine:

<
asp:GridView
ID="PublicClassifiedsSamplesGridView"
runat="server"
AutoGenerateColumns="False"
DataKeyNames="AutoNumber"
DataSourceID="PublicClassifiedsSamplesSqlDataSource"
CellPadding="4"
ForeColor="#333333"
OnDataBound="PublicClassifiedsSamplesGridView_DataBound"
>
<Columns>
<asp:TemplateField
HeaderText="Click for information">
<ItemTemplate>
<asp:ImageButton
ID="ThumbNailImageButton"
runat="server" Width="100px"
PostBackUrl='<%# string.Concat("~/Classifieds/DetailPage.aspx?AutoNumber=",Convert.ToString(Eval("AutoNumber")),"&amp;FlagForm=NoSubmitted")
%>'
ImageUrl='<%# string.Concat("~/UploadedImagesClassifieds/",Convert.ToString(Eval("AutoNumber")),"Pic1.jpg")
%>'
/>
</ItemTemplate>
<ItemStyle
HorizontalAlign="Center"
Width="100px"
/>
</asp:TemplateField>
<custom:LongTextField
DataField="TListingComment"
Width="150px"
Height="70px"
HeaderText="Listing Comment"
HtmlEncode="false"
/>
</Columns>
</asp:GridView>