Concatenate ".jpg" to a Binded value

I have this line on a website made with c #,

 <p><asp:Image id=Imagen1 runat="server" ImageUrl='<%# Bind("Id_producto") %>'/>  </p>

And I need the ImageUrl value to be the data that comes from Bind, plus the .jpg extension, but I do not succeed, I tried with "+" .jpg ", with + '.jpg', but nothing.

Thank you.