Cl3ric0l's first post is primarily a warning, not an insult. If a piece of artwork doesn't have a license attached to it or it has a license prohibiting usage then it's probably illegal to reuse. Modifying a piece of digital art, whether it be an image, photo, or render that doesn't have a license is considered stealing.
Most of the time no one's gonna issue a takedown notice but if the artist were to see you selling it, it's definitely gonna provoke action. Since he's selling for Torn dollars it's probably not gonna lead to legal consequences but the chance is definitely there(even if it wasn't illegal you're still doing something immoral by using someone's work in an unintended way).
I dunno how much of the work on here violates licensing laws but if there's a Creative Commons zero license attached usually you don't have to attribute the original artist and you're free to use their work commercially. Different licenses have different restrictions. It's not about how much or how little you modify it. It's about how the author intended his art to be used.
I'm no lawyer so I couldn't tell you how this works in different countries.
All I'm saying is, it's not just immoral to use work without permission; it can be illegal.
For this case, the original artist is most likely Wiebke Scholz:
http://conceptartempire.com/item-shop-interior-art/http://aeyol.cgsociety.org/art/concept-photoshop-art-simon-sorcerer-background-2d-magic-shop-1223452He created this piece of art for a game called Simon the Sorcerer: Between Worlds. I don't believe this game will ever come out but the artist did create this piece for money and has chosen not to include a license permitting free usage.