I've written about plagiarism in infographics before, in my old website. I believe that I'm particularly flexible in this regard: Do you want to copy any of my graphics? I'm fine with that. As Austin Kleon explains in his wonderful Steal Like an Artist, most innovations are the product of mashing up existing ideas to create a new object. Similarly, most graphics are inspired by other graphics, in one sense or another.
The fine line between what's appropriate and not, however, lies in attribution. Are you going to use somebody else's ideas? Mention her. Are you going to use —or repurpose— somebody else's graphics? Some would say, ask for permission first. But I'd argue: Perhaps you could go ahead and do it, but at least give that person proper credit.
This article was published in .Net magazine online. See figures 3 and 7 in it. Originally, their sources were not there. Compare them to the images below, taken from The Functional Art. I drew them with Illustrator when I was writing the book (click on the picture to expand it):
They are basically the same. They have been copied. Just the arrangement and the colors have been slightly tweaked.
To be clear, I'm not the "owner" of the ideas contained in those graphics. It's debatable if ideas can be "owned" at all, in the first place. Besides, those graphics are based on several sources: The first one, on William Cleveland's and Robert McGill's work, and the second on Colin Ware, Stephen Kosslyn, and others. Perhaps I can claim some originality in a detail in the first graphic, the "allows more accurate judgements" and "allows more generic judgements" thing in the vertical scale, which I believe I came up with (I may be wrong.) In any case, I'm fine with anybody using those images as inspiration, and even copying them —my publisher may disagree with this,— but it is wrong, completely wrong, to just use somebody else's work as if it were your own. Always try to mention your sources correctly. Be careful with this. Avoid mistakes and omissions. And listen to this educative podcast in Datastori.es.