You can use image tags in the description side of the "add an item"--"links" area and any url in the "Website Address" side to produce clickable images.
Description
Web Address (URL)
<<>img src="url of image" width="??" height="??">
Type a url of a website here
Results of using the codes from the table are below:
Note: Images can also be made clickable links by using standard html codes, instead of using Webtv's "add an item"--"links" area:
<<>a href="url of website or image">
<<>img src="url of image" width="??" height="??">
<<>/a>