As mentioned in the FAQ, I always contact authors before showcasing their artwork. With regard to Eternal_Origin_by_j4m3sb0nd.jpg it's a good thing that you brought it up because I double checked my records and it seems this image was included by mistake. I have just sent an email to the author explaining the situation and asked for their permission to use it.
Human-error like this happens every once in a while but it is my policy to *always* ask for permission before using any artwork. Please let me know if you find any other violations in the future and I will correct them as soon as possible.