Most areas that allow you to post images in the site will also allow you to convert the image to a hyperlink.
When working with an Image module, look for the hyperlink option in the toolbar:
When working with an image you've inserted into a Text module, select the image and click the Insert Hyperlink option in the page's toolbar:
Clicking the button will allow you to set up the target location for the linked image. As with all links in the site, you'll be able to enter a URL or select from your Site Map and Lockers.