How to setup Internet Expense receipt attachment file as URL link

We are trying to use the attach receipt image file in Internet Expense.  The option of the attachment are file, URL and text.  How do I setup to use file via URL?  When I type the actual file link and got a page not found error message.  Where is the file from URL link stores after been attach to the Expense Report?  Is it still in the URL site or is it in the FND_LOBS?  Is there a document on how to setup URL file link?  Also,  it there a way to limit the size of file and the type