Most image replacement (IR) techniques work by displaying a background image of text and shifting the real text out of view. This is fine unless you have images turned off, in which case you will see neither the graphical text nor the real text.
checkImages() function should be called by a
window.onload handler. The function determines whether images are turned off by checking the
offsetWidth of an existing inline image – the logo in this case. If the
offsetWidth of the image element does not equal the known width of the image then images are assumed to be turned off and the IR technique (Phark in the case) is reversed to reveal the heading text.