In a presentation on research methods I gave some years ago in an international meeting, I referred to an in-progress study I was conducting as an example. The study consists of data from different social media (n=2,080 interactions) produced spontaneously as reactions to a topic I was investigating. However, a British colleague drew my attention to getting the consent of all the writiers on these media so that my study would be ethical! I reacted immediately and said: "this is another issue that can be discussed later!" but, actually, I was wondering how I could get such consents from so many unknown people!!
When you are processing data that has become public (video, podcast, photos, data on social media, written products such as blogs, ...) for research purposes and you cite the source(s) of the data at hand, do you still have to get consent to be ethical?