Write ALT text for your image. You may want to indicate that more information is available by following the d-link, using something like ALT="Graph of Sales Figures - See [D] for more information".
Immediately following the image, link to a page (or, via a named anchor, to another location within the same page) that includes a description of the image's content. If you are linking to a separate page, it's a good idea to include a link to return to the calling page.
In the anchor tag used to link to the description, use the TITLE attribute to identify what the link is to. For example: TITLE="Detailed information on the sales figures graph"
If you wish to hide the descriptive link, use an inline style change to match the font color to the background color. If you don't use style sheets, then the FONT element (although deprecated) is also an option.