Unfortunately, only photos that are hosted some place can be uploaded via the hyperlink. The benefit of this is that you can reference photos or videos that are hosted anywhere. You're not limited to referencing them from Flickr or Picasso.
If there is a photo on your website (or is hosted on your domain) you can right-click that photo and click 'Copy Image URL' to retrieve the hyperlink.
How to add pictures to a form outside of Flickr or Picasso
Written by Katrina Grein-Topken
Updated over a week ago