Poking about for readings for a course in Persuasion that I am teaching this fall, I came across this WikiBook project (similar to wikipedia but used for collaborative book productive, especially textbooks). Overall the book serves as a basic introduction to Visual Rhetoric, but the chapter of special interest for CommEthics folks might be this one, on the ethics of visual rhetoric:
http://en.wikibooks.org/wiki/Visual_Rhetoric/Ethics_of_Controversial_Images