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 simple hover over the image and using the pencil icon and 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 done, upon click your image will direct to the URL you have entered. More on this here.