Let's get the chant going, shall we?
"Fair Use Doctrine! Fair Use Doctrine! Fair Use Doctrine!"
The point is REALLY, exceptionally simple: a DMCA Cease and Desist notice MUST be served, FIRST, before any copyright infringement case can be made.
However, since the use of a copyrighted photo in the context of education, artistic discussion,or criticism, is SPECIFICALLY ALLOWED as an ***EXCEPTION AGAINST THE PROHIBITION OF THE USE OF COPYRIGHTED MATERIAL***, the rule against "posting" copyrighted material represents, as The_Traveler stated above, "boogey-man gonna getchas in the dark responses to simple reality."
As to the implied "immorality" of using copyrighted images in a non-profit manner, for purposes of commentary, discussion,education,and so on...oh,puh-lease...United States copyright law is perfectly clear that there is a clear and obvious NEED TO ALLOW critical, public discussion of a broad range of copyrighted works. As an undergrad, I spent ten weeks studying copyright laws, issues, and cases at the University of Oregon school of journalism. Every time I see this site's rules and policies on copyright issues, I think of how absolutely outrageous the entire situation actually is. This site operates under a rule basis that is, quite simply, ridiculous, and well...fill in any one of a hundred pejorative pairs here: ___________________ and ___________________.
Of course, this is not my web forum. Tons of misinformation and lunacy makes its way into rules, policies, and even social customs--all over the WORLD, and not only here, on TPF! The fact that a rule might be foolish, idiotic, or contrary to actual realities (scientific, legal, or historical,etc.) if of little consequence for those who make the rules. Those who must follow the rules, and those who must enforce said silly rules, have it the hardest. The bottom line is that TPF has a fundamentally unpopular set of rules that apply to the use of copyrighted works; this set of rules is based on a hugely flawed understanding of the MOST-basic aspect of the Fair Use Doctrine. It is a simple Draconian measure--one that people who are familiar with United States copyright law and fair use understand to be _______________ and _______________ ,and maybe even ______________ (fill in a trio of disparaging words, according to your own sense of flair and style! You KNOW you want to!).
BUT, and this is the most-important thing to keep in mind: "Them is da' rules!". "My house, my rules." "It's my way, or the highway." "Like it, or lump it." "It is what it is." "Them's the breaks." "Too bad, so sad."