When undertaking project research there are a variety of sources that could be used: books (or google books online) can come in the format of text/research books, documentation books, or even autobiographies. Information online can come from known establishments - such as galleries and museums, magazines etc - or even from blogs.
We were given the task to research methods of 'protest graphics', finding at least two distrinct research sources and evaluate each accordingly:
Disobedient Objects, Catherine Flood (2014)
'The book explores the material culture of radical change and protest - from objects familiar to many, such as banners or posters, to the more militant, cunning or technologically cutting-edge, including lock-ons, book-blocs and activist robots'
This book was published alongside an exhibition of the same name that showed at the V&A in London from July 2014 to February 2015. It documents a broad range of materials used in protests and therefore gives a wide picture or protest movements through the ages. The book comes from a reliable source as the V&A has a known reputation.
'Beauty is in the Street: The Power of Protest Posters', Justin McGuirk, 2011
'Beauty is in the Street' was an article published on The Guardian website detailing the Paris Uprising of May 1968, and the role that street posters and flyers played to gather public and media attention. Again, the article comes from a reputable source, but The Guardian has known left-wing political views and so information they publish may have a biased attitude.
http://www.theguardian.com/artanddesign/2011/may/23/beauty-in-street-posters-protest