It might seem basic common sense, but more often than not, clients are surprised when I remind them that they need to ensure they have proper permission for reuse of materials, as well as making certain that the rights holder receives proper credit. This is important for many reasons, the least of them so that the reader or observer of the material can refer back to the original source material if they so wish.
I came across this the other day in my readings, and found the credit line amusing. The person who posted this material is blatant in stating that they did not receive permission to reuse the illustration, but they do provide credit back to the original rights holder:
What alarms me about the above "credit" and review is the accompanying illustration. Although you cannot see it for yourself, you will have to trust me here. While using a thumbnail of the cover of a book is usually deemed to be acceptable practice for reviews, taking an image off of the cover and posting that independent of the cover design is not.
As this particular piece is a review (providing critique of the original), it is true that this usage would be considered fair use, and the review's author would be unlikely to face a claim of copyright infringement.
It is also appropriate that the author of the review provides credit back to the original source, as well as information on how the interested reader might buy the book. But it doesn't excuse them from not getting proper permission for the reuse of the illustration out of context from the original cover.
Remember, even when the reuse seems to be innocent enough, it remains in the rightsholder's power to deny permission for any use. If you don't ask first, you might find yourself facing a copyright infringement suit.