A link composed of an image as opposed to actual HTML text. The format for a image link is:
<a href=”link-goes-here.html”><img src="image.jpg" alt="optional alternate text" /></a>
In the above example “image.jpg” is the link image. The optional alt tag is used to convey information about the image to search engines, screen readers and other non-visual devices.
An image link is generally considered less valuable for SEO purposes than a text-based link.