No. WinSCP does not know it. Only your webserver knows actual mapping from filesystem paths to URL addresses.
For example if your file is stored in path
/home/user/public_html/folder/img.gif on server
www.example.com, the URL can be
http://www.example.com/~user/folder/img.gif. But it can also be in completely different path or even on different server. WinSCP cannot know this.
If you know the mapping from filesystem path to URL address, you can make your own custom command to map the paths for you. You need to use some scripting language for this. For example Perl or PHP.
See example how to implement such custom command using PHP script.
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