Q: Where I can find a free footage to make my presentation in class more engaging? My students are copiyng images from Internet for their projects. How to make sure that they are copyright free?

A: In a situation when students are assigned to use the pictures for power point presentation project I will advise students to search in public domains.

How to use Creative Commons to find free images, audio and video tutorial: http://www.youtube.com/watch?v=YvsbJaJeFGY
The instructions are at Creative Commons wiki page: http://wiki.creativecommons.org/Public_domain
and here: http://wiki.creativecommons.org/Frequently_Asked_Questions

Not all the links are working but it is a good place to start your search for free footage.
CC free video search: http://wiki.creativecommons.org/index.php?title=Special:Ask&offset=50&limit=500&q=[[format%3A%3AMovingImage]]&p=mainlabel%3DName%2Fformat%3Dbroadtable&po=%3F%3DName%23%0A%3FMainurl%3DWebsite%0A%3FSize%0A

and films: http://wiki.creativecommons.org/Video

Example: http://wiki.creativecommons.org/Blip.tv
http://blip.tv/