1.  In the content property, enter the field or formula that defines the appearance of the checkbox.

2.  Select the picture for 'True', i.e. if the calculation of the content formula returns 'true'. Select one of the internal pictures or select an external picture. You can adjust the frame and icon color of the internal pictures.

3.  Now select the picture for 'False' and 'NULL'.

 

Please also refer to the chapter titled "Overview of Properties".