This was the thought that bothers me also. What if someone just downloaded a stock image and just plainly edited them with their own skills in photoshop and published it in the internet. Imagine if they just gave it at a high price and someone bought it.
It's insane. This is no different than making money "out of thin air". Anyone can simply download an image from the web and sell it as their own for profit. I've seen many "digital arts" being sold for millions of dollars (USD) on the Blockchain, when they really have no intrinsic value. The hype is still on-going so the situation will only get worse. At least, the idea is there. Making it a success is another story. I hope NFTs don't see their fate like ICOs where governments destroyed them with fierce regulations. As long as the industry has legitimate use cases, there should be nothing to worry about. Just my opinion
