Maybe it's the time of day, but "This will not be checked if it's a valid URL" reads to me as: "If this parameter is a correct URL, it will not be checked".

Maybe you can say that this method will not verify that the URL does not point to sensitive information on the filesystem, such as /etc/passwd, and thus could end up generating an image of the password file if not used properly.

To reduce the hazardous impact, we could restrict that the file meet some kind of criteria, such as it ends in `.html`.