This is the techniques to be followed:
1. Search if there's any link "links", "additional sites" "related links" and so on.
2. Check for references (Do you see footnote numbers or links?). Explore the references to find out if they are real, reputable, and scholarly.
3. Take a look at the page's publisher (first part of the URL). If the author has some publications on the web, look at the bottom of the articles to see if there is any copyright information or permissions to reproduce.