You can link images within pages to external sites. To do this on a page, click into the page and click edit page content in the floating remote. Another way to get there is to simply hover over the image, click the pencil icon and then click edit page content.
Hover over the image you want to add a link to, and click add link. Insert the desired URL link in the pop up.
Once you've completed the steps above, you can click on your image to be directed to the URL you have entered. More on this here.