Copyright is interesting, but there is also trademarking involved when you start using trademarked images, logos, and even word combinations. It is perfectly legal for me to start with art and photographs found on the internet and use them to create a cover for a book, as long as I am not taking the untouched art and just pasting my title on it. Also, if I am using any kind of trademarked image within my art I am probably in trouble. As a matter of fact, the original title to my book was "The Popsicle Factory", but before officially publishing I looked into whether I would be in trouble using the word "Popsicle" in my title for a commercially available book. I found that the company that owns the trademark is very active in suing anyone who uses it (as well as a number of other "icle" words) and in fact there was a "fair use" trial quite a number of years ago that the owners of the trademark won. I decided it was probably a bad idea to use the word in my title, so I changed it.
If someone read my book and decided to write something with a similar story line, similar characters, a similar cover, and a similar title, it would be difficult to sue them for copyright infringement. There is a lot of gray area when it comes to copyrights. However, if someone copied my book word for word, changed the character's names, the title, and the cover art, they would be in clear violation of copyright. I could take a concept straight from any story, movie, or television show and write my own book on it and be perfectly fine legally (although it might gain some criticism for not being original) because it is my words. Gatsu created a piece of art and hence he is protected by copyright. Someone selling that art unchanged is a violation of his rights. Just because Gatsu is subject to a lawsuit because he used a trademarked image doesn't change the fact that his work is protected. If the seller started with the same artwork and logos that Gatsu started with and then created his own work from it, he would likely be OK, particularly since something as generic as a control panel layout can't really be copyrighted.. it is too common. Of course, then he would still run into the issue of using a trademarked image in a commercially available piece of art...
FYI, I pirated a lot of stuff when I was younger. I had the attitude that if it could be copied easily I should be free to do so. Plus I didn't have the money to buy things I wanted. Sure, it was stealing, but I didn't see it that way as it was all ones and zeros. My view changed over the years, and I pay for everything I get now. Karma kicked me in the butt though when I found out my book was posted for free on several websites. Someone bought it, ripped it from the DRM protected format, and put it up as a PDF. The site I found it at even had a bartering system with a currency people could use to pay "bounties" for working links to pirated materials they are interested in, and someone paid to find my book for free (and someone provided it and was paid for their time). I wrote some letters to the website owners and my book was promptly removed. I am sure it is still out there on the more private pirate file sharing sites, but the way I look at it is those people who are going to download it there are not going to ever buy it anyway and those sites don't come up on Google so paying customers will never find it and have to buy if they want it. This other site was sitting on page 1 of a google search, right below the link to my book on Amazon, so that was hurting sales.
Trust me, I know the feeling when you find YOUR work being handled in a way you never wanted, but you fixed it so take pride in the fact that it was good enough to make money for someone. Once I accepted the fact that people would pirate my work, I realized it feels pretty good to have created something good enough for people to WANT to pirate.