How to determine which checkbox is checked in Repeater with imagebutton and checkbox insdie

Hi I have a repeater with image button and checkbox inside
How can I detect which check box is checked

<asp:Repeater ID="rptrUserPhotos" runat="server" OnItemCommand="rptrUserPhotos_ItemCommand" > <ItemTemplate> <asp:ImageButton ID="ImageButton1" runat="server" ImageUrl ="<%# Container.DataItem %>" style="height: 100px;" CommandName ="test" /> <asp:CheckBox ID="CheckBox1" runat="server" /> </ItemTemplate> </asp:Repeater> <asp:Button id="btnDeleteImage" runat="server" Text="DeleteImage" OnClick="btnDeleteImage_Click" />