I have noticed that a lot of questions and answers include images and quotes without attribution. In many instances images are used that aren't licensed for reüse1. In some instances I have found large blocks of text copied-and-pasted without it being quoted or clearly attributed2; this is typically considered to be plagiarism. I've been going through and making at least some attempt at fixing these and gently reminded people to provide proper attribution. It does feels like a game of whack-a-mole at times though. How should this be handled?
2 The initial version of one answer for example. Initially I honestly thought that it was original writing. It wasn't until several hours later that I discovered that it was almost entirely a quote from an article.