An important clue to the origin of the work lies in the site's URL or domain name. The URL is a good indication of who has published the material. If it is linked to a university, research institute, or governmental association – with the URL extensions .edu, .org, or .gov. – you may be on the right track. Note that you still need to review the information you find on these sites.
Watch this video gives a quick intro to the information you can learn from the URL.