What you need to do, is in the HTML editor, associate the link with your image. The exact steps will depend on the editor you are using, but here is what works with TinyMCE using Firefox (editor choice can be changed in Administration, Site Settings):
-
In the editor, right-click on the image, and select Insert/Edit Link.
-
Paste your link into the Link URL box.
-
Click Update
-
Save your changes.
Now when you mouse over the image you'll see that a click will send you to the target URL.
Hope that helps,
Jamie