how to generate an image from a panel on the webform page

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ASP.NET

how to generate an image from a panel on the webform page? These are some items like labels on the panel. How to resolve the problem, please help me, thank you very much.

that's the panel's html code. I want to get the image from the render panel.
generate a image from a panel webcontrol.

<asp:Panel ID="legendPanel" runat="server" Visible="false">
         <div style="position:absolute;top:80px;left:80px;">
            <table border="0px">
              <tr><td colspan="2">单位:mm</td></tr>
              <tr>
                  <td>
                     <asp:Label ID="color1" runat="server" Text="" Width="30px" Height="10px"></asp:Label>
                  </td>
                  <td align="left">
                    <asp:Label ID="Lable1" runat="server" Text=""  Height="10px" >
                    </asp:Label>
                  </td>
              </tr>
              
              <tr>
                   <td>
                     <asp:Label ID="color2" runat="server" Text="" Width="30px" Height="10px">
                     </asp:Label>
                   </td>
                   <td align="left">
                     <asp:Label ID="Label2" runat="server" Text=""  Height="10px">
                     </asp:Label>
                   </td>
              </tr>
              
              <tr>
                    <td>
                      <asp:Label ID="color3" runat="server" Text="" Width="30px" Height="10px">
                      </asp:Label>
                    </td>
                    <td align="left">
                      <asp:Label ID="Label3" runat="server" Text=""  Height="10px">
                      </asp:Label>
                    </td>
              </tr>
              
              <tr>
                    <td>
                      <asp:Label ID="color4" runat="server" Text="" Width="30px" Height="10px">
                      </asp:Label>
                    </td>
                    <td align="left">
                      <asp:Label ID="Label4" runat="server" Text=""  Height="10px">
                      </asp:Label>
                    </td>
              </tr>
              
              <tr>
                    <td>
                    <asp:Label ID="color5" runat="server" Text="" Width="30px" Height="10px">
                    </asp:Label>
                    </td>
                    <td align="left">
                    <asp:Label ID="Label5" runat="server" Text=""  Height="10px">
                    </asp:Label>
                    </td>
              </tr>
              
              <tr>
                    <td>
                      <asp:Label ID="color6" runat="server" Text="" Width="30px" Height="10px">
                      </asp:Label>
                    </td>
                    <td align="left">
                      <asp:Label ID="Label6" runat="server" Text=""  Height="10px">
                      </asp:Label>
                    </td>
              </tr>
            </table>
         </div>
</asp:Panel>