ToggleButton Properties:

•TargetControlID - The ID of the CheckBox to modify

•Image Height\Image Width - The height and width of the image

•CheckedImageUrl - the URL of the image to show when the toggle button is in the checked state.

•UncheckedImageUrl - the URL of the image to show when the toggle button is in the unchecked state.

Code:

 <%-- ScriptManager control manages client script for AJAX enabled ASP.NET pages.This enables partial-page rendering and Web-service calls.You have to used this if you want to use ajax control--%>
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
  
 <%--Add the togglebuttonextender and one checkbox--%>
<cc1:ToggleButtonExtender ID="ToggleButtonExtender1" runat="server" TargetControlID="CheckBox1" UncheckedImageUrl="~/Unchecked.png"
CheckedImageUrl="~/Checked.png" ImageHeight="60" ImageWidth="60">
</cc1:ToggleButtonExtender>
  
<asp:CheckBox ID="CheckBox1" runat="server" Text="Do you want to select?" />

Run the project

Images hide the checkboxes to show the checked and unchecked state.