Hi,
Try this if could help...
Change your code from:
<asp:TemplateField HeaderText="Image">
<ItemTemplate>
<asp:Image ID="Image1" runat="server" ImageUrl='<%# "HandlerCategory1.ashx?ID=" & Eval("ID")%>' />
</ItemTemplate>
<asp:TemplateField>
to example:
<asp:TemplateField HeaderText="Image">
<ItemTemplate>
<a href='PhotoDetail.aspx?id= <%# Eval("ID") %>'>
<img src='<%# "HandlerCategory1.ashx?ID=" + Eval("ID") %>' alt='<%# Eval("Picture") %>' />
</a>
</ItemTemplate>
<ItemStyle HorizontalAlign="Justify" VerticalAlign="Middle"></ItemStyle>
</asp:TemplateField>
Regards,