I'd like to suggest the ability to upload an image from your dropbox account. Not via URL, because that would be easily abused, but add a hook into the Dropbox API that allows you to add a file or folder found in your dropbox.
I'm not sure if that's the URL you'd need or not. Just like a site that lets you login with google, there's a method for doing this with Dropbox and allowing the site to access files. I believe you can even make it request read only access or maybe even better, make it request access to a specific folder only. (Like, you could create an FN folder in the main Dropbox folder, so that any files there are available to upload on FN when you load the upload section and click "from dropbox".)
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