In Windows 7 (and perhaps earlier), the default "Open File" dialog box allows you to type a full URL into the "File name" section as if it were a file path, e.g. "http://www.example.com/pic.gif" instead of "C:/windows/pictures/pic.gif". When uploading a file to a website on the client side - say, an image - this allows the client to upload a picture located on a server accessible via the URL instead of downloading the image, saving it locally, then referencing the local image in the "Open File" dialog.
It's a great option for Windows users. I have three separate questions:
What is this procedure formally called? How do I describe this succinctly so that my searches for more information are fruitful?
Can something similar be done in Mac OSX, Chromium OS, or a Linux environment?
If so, how?