(This probably doesn’t work anymore.)
Dropbox will create a link to an image that looks like https://www.dropbox.com/s/8dlmxjlf3jkd5zd/DSC09789.jpg?dl=0. When I follow it, I get a page with the image in it, but not just the image itself. The link can’t be used to place an image in an HTML page.
To make such a link, change https://www.dropbox.com to https://dl.dropboxusercontent.com.
https://dl.dropboxusercontent.com/s/pd92mem44ojeuwl/DSC01141-diptych.jpg?dl=0