You can not add CommandArgument/Comamnd Event to Div/Panel control
Instead of it you can add on LinkButton / ImageButton or Button to fulfil your requirement and Add that button to Div
<div id="Div1" class="image_stack">
runat="server">
<asp:linkbutton id="linkButton" text="text" commandargument="1" commandname="GetAlbum" runat="server" xmlns:asp="#unknown">
<img id="Img1" class="stackphotos photo1">
<img id="Img2" class="stackphotos photo2">
<img id="Img3" class="stackphotos photo3">
</div>