I think this is going to be a problem because the FTP directory lies next to the public_html directory where the webpages are saved, not sure about this, but I think in this case you cannot access the FTP directory from the web, it is above the top-level directory, only visible in FTP client.
I would create a new folder in public_html called grLevelX and upload the images there so that it is inside the public_html and can be viewed on the web.
But wait for what Ken says, he is the expert on this.