[WDHewson]

It may not be stolen at all. It may have been your gift to the world via the internet.

And if you put the image on the "net" without copyright, then it is likely a gift.

Also, lots of copyright law exempts limited use by educators and schools.  Was it an unpaid educational TedTalk?

Very little of this is accurate under US or European copyright laws.

Using an image for education is not exempt from copyright laws, Journalistic purposes is.

All images are copyrighted, uploading them to the internet in general does not relinquish that copyright.  You do have to beware of which sites you put an image on and what their terms are.  You do not have to register an image for copyright laws to protect it.

Do some homework!!

The Classroom Use Exemption
Copyright law places a high value on educational uses. The Classroom Use Exemption (17 U.S.C. §110(1)) only applies in very limited situations, but where it does apply, it gives some pretty clear rights.

Obama in class CC by-nc Gilkata 
In-class viewing is a public performance, but it's permitted under the Classroom Use Exemption
To qualify for this exemption, you must: be in a classroom ("or similar place devoted to instruction"). Be there in person, engaged in face-to-face teaching activities. Be at a nonprofit educational institution. Sounds a little restrictive?