How do you detect when your photos are used without copyright permission?

How can you tell when your images are being used without your consent?

In other words, How can you find your images being used in the real world?

I imagine the most prolific medium using images irrespective of copyright would be the web, then print, and so on... Are there ways you can detect your images' usage? If so, how do you go about it?

Answer

I don't know about print, but for the web.. http://www.tineye.com/ is a reverse image search used for these kinds of purposes.