One legitimate way to get more keywords into your web page, and at the same time make it more accessible, is to use the alt attribute in image tags. Another less-often-used method uses the title attribute in the anchor tag for links.
Here's how to use both techniques when using an image as a link.
With a bare minimum of coding, you can get away with something like this:
<a href="contact.shtml"><img src="images/contact.gif /"></a>
For better accessibility, add the aforementioned attributes, like so:
<a href="contact.shtml" title="Click here to send us feedback about our blue widgets."> <img src="images/contact.gif" alt="Click here to go to the Blue Widgets Contact Us Page." /> </a>
The title tag does not need to mention what's in the image, and can just give the call to action and the keyword. The alt tag should be used to also convey the information in the image, so that users who can't see the image know what it's about. Now you have doubled the keyword phrase "blue widgets".
See it in action: Hover over the image link below. You should see my title in the hovertip. And the text in the alt can be "seen" by text readers used for the visually handicapped.