Scenario 1:

You have found some good information at a government web site. May you copy the information and use it liberally in the classroom?

Answer: Information at a government web site is in public domain and considered common property. Therefore, you may distribute the information without fear of copyright infringement.

Scenario 2:

A student has been assigned to make a personal Web page for class. The student chooses baseball as a topic but doesn't have any pictures. They do a google images search and find some pictures to use. There is no clear statement anywhere saying they are copyrighted. Can the student go ahead and use these pictures?

Answer: One should always first try to contact the site owner where the picture is housed (after clicking on it from Google) and contact that person to get permission. Also check if you can alter the image if you desire to do so. That said though, students doing work for a class are actually covered by the Fair Use act:

Students may:

• Use digital images in an academic course assignment such as a term paper or thesis, or in fulfillment of degree requirements.
• Publicly display their academic work incorporating digital images in courses for which they are registered and during formal critiques at a nonprofit educational institution.
• Retain their academic work in their personal portfolios for later uses such as graduate school and employment applications.

see http://www.ninch.org/ISSUES/COPYRIGHT/FAIR_USE_EDUCATION/CONFU/DigitalImages.html#edschol