Adding gallery images from external file automatically

I would like to have a file of images, not on SS that I can add images to easily that will automatically populate a gallery block and update each time I add or delete them.  Dropbox might work but you have to manually sync from within SS.  Is there any other way to do this?  (On my site, the "On The Rocks Tables" get different tops, all unique.  We need to have the current tops available for the customer to choose from and easily keep it updated with additions and deletions.)  Appreciate any help and suggestions!

The only way to achieve that would be if you were in Developer mode and set up an FTP server, this is most lively not a good suggestion as that step comes with many downsides. Hopefully Squarespace will make managing uploaded files easier in the future, but until then there's not a great solution to match up a gallery and a local folder.