To provide a background image or a watermark, you can assign values to <body> attributes in the configuration file; for example:
[Attributes] body= bgcolor="white" background="yourimage.jpg"
If you are targeting only Internet Explorer (as for HTML Help), to keep the image from scrolling with the text you could add:
... bgproperties="fixed"
All attributes and values must be on the same line, regardless of line length.
A better alternative would be to use CSS. There you could also specify that the image is to be centered, not tiled, which is probably what you would want for a watermark:
body { background-color: white ; background-image: url(yourimage.jpg) ; background-repeat: no-repeat ; background-attachment: fixed ; background-position: center }
body { background: white url(yourimage.jpg) no-repeat center fixed }