Find the image you want to upload and select. Once it has been successfully upload, it will appear among the other files - make sure it is highlighted and make sure to check 'OPEN IN A NEW WINDOW'. 

Once you have your activated link, click 'SAVE' on the page editing window. 

 

Now, click on the activated link which should open up into a new tab.

Copy and paste the url into the Vertical Response url link.