HTML Help question.

I have implemented help in my MFC App, so that when a dialog is displayed and the F1 key is pressed, HTML Help is invoked and correctly displays the help for the dialog displayed, it also displays the table of contents and highlights the correct title. The HTML file has some images and mostly text.
My problem is the following...on most PC's, once the F1 key is pressed, the images aren't displayed; HOWEVER if I single click on the title in the Table Of Contents...all is well.

Any ideas/suggestions.
Thanks,

Roberto