Screenshot of a public web site and posting it to a blog copyright violation or Fair Use?

Is taking a screenshot of a public web site (like Google or Flickr) and posting it to your weblog or in a presentation considered copyright violation, or does it fall under Fair Use?

1. The purpose and character of the use

2. The nature of the copyrighted work

3. The amount and substantiality of the portion used in relation to the copyrighted work as a whole

4. The effect of the use upon the potential market for or value of the copyrighted work

full article and source:
http://lifehacker.com/193343/ask-the-law-geek--is-publishing...