"... the sources were not cleared by the publisher"
Here's an extract from an online course introduction. The course is devoted to the role of the media as a means to influence people's ideas, perception and knowledge of history. My question is: what does "clear" mean in the paragraph below? Does it say it's not clear where the images come from or that the images themselves are not clear (i.e. blurry or soomething)? Thanks in advance!
"A key issue is the quality of your source: you will find a number of images I refer to in the course on the web, but some of the sources were obviously not cleared by the publisher. Therefore, I have not linked directly to them. Judgement over the sources you consult and use is a critical aspect of historical research, and the course will touch on these issues with respect to the manipulation of images in the twentieth century, with the odd twenty-first example thrown in as well".