Open a project (.hhp) file, click the Contents tab, and then click Contents Properties.
Contents Properties
Defines the general appearance of the table of contents.
Select the Use custom images from a file check box.
In the Image file box, enter the path to an icon strip bitmap (.bmp) file that contains the images you want to use instead of the default images.
Save and close the project file.
Reopen the project file.
Note
If you want to use folders and pages instead of books and topics, click Contents Properties, and then select the Use folders instead of books check box.