go to joomla backend and go to modules>site modules and press “New” at top right.
Scroll down to Custom output and paste this there:
<body>
<a href="your link location goes here"><img src="full image path goes here" width="image width here" height="image height here" border="0" /></a>
</body>
</html>
If i do this as below i get the joomlart logo and links to joomlart frontpage
<body>
<a href="http://www.joomlart.com"><img src="http://www.joomlart.com/templates/default/images/logo.gif" width="295" height="70" border="0" /></a>
</body>
</html>
Remember to set a name on the module, position ordering and access level.