You haven't told us what
"not working" means. But you shouldn't need the table at all:
<asp:ListView ID="ListView1" runat="server" DataKeyNames="PhotoGalleryID" DataSourceID="SqlDataSource1">
<LayoutTemplate>
<div style="width:100%;overflow-x:auto;">
<div id="itemPlaceholder" runat="server"></div>
</div>
</LayoutTemplate>
<ItemTemplate>
<div style="width:100%;">
<img src='<%# Eval("PhotoName", "~/PhotoGallery/{0}") %>' alt="" style="display:block;margin:0 auto;max-width:100%;" />
</div>
</ItemTemplate>
</ListView>