How to address the issue of the widespread use of protected material in informal publications? One thing that always bothered me is the liberal use of protected material in informal academic publications (for example Powerpoint presentations, handouts and internal reports rather than published papers).

It seems that the "everything on the Internet is free" attitude is also widespread in the academic world. And while I regularly spend a considerable amount of time either creating the graphic material I need or search for it on the Internet, nearly everybody else is not even thinking about it. Need a nice picture of a sunset or a little fish to include in your graphic? Just google and use the first one, without thinking twice!

This does not happen on single occasions only, I've made that experience in several countries, working in different environments.

Sometimes, among co-workers and friends I raise this issue and am usually met with understanding. Most of them see the problem with the additional time they need to spend to search for relevant material or the creation of an appropriate space to include copyright notes or references to graphic material. Some also mention that it would be considered unprofessional including a user name on the Internet as the source for their imagery.

My questions therefore is, how do I sensibly raise this issue among supervisors (which may consider this a waste of time) or an unknown crowd, especially considering above-mentioned criteria?
From an ethical point of view, I think most people can still sleep well despite taking the first fish from Google from time to time. 

From a legal perspective, it depends on your jurisdiction and the license of the image. As Jeff points out, it's often fine in many places.

You should define your goals (ethics vs. legal), and act accordingly (which is my case would be do nothing).