If you just want to add the image, not do anything fancy with it, you can use inline HTML in Simple XML. That way you do not need any JavaScript or StyleSheet files.
<dashboard>
<label>Picture in dashboard</label>
<row>
<html>
<img src="level3_description.png" />
</html>
</row>
</dashboard>
This would add your picture as a panel.
For more information check out the Build Dashboards with Simple XML section in the manual.
Cheers,
