Let me put it this way...
I am a writer. If I publish a book, and someone scans or types it up on the internet, so that people can "just download it on the internet" rather than paying me... I'm loosing money. It is the same to my pocketbook, as if I had been paid that money, and someone stole it from me. Either way, I had the right to that money, and yet... I do not have it.
By getting "free stuff" on the internet that belongs to living artists, you may not be physically stealing the work itself, and you may not be breaking into their home and stealing their wallet, but the fact of the matter is, if you want to get that work by totally honest means, you would, in fact, have to pay for it. Which you are NOT doing, if you just "get it on the internet".
Evil is defined as a lack of good, and in this case, you have a lack of good that is due to the artist, being rendered by people who SHOULD be paying for that work.
Even if someone does not break into my home and steal my computer with my stories on it, if I publish a book and someone puts my story online for the world to have for free, I will be just as cheated as if they had robbed me of money that was in my hands already. People would be enjoying my work, and I would NOT be enjoying the pay rightfully due to me for it. I would feel sorry for anyone, of course, who could not afford to buy it. But the fact of the matter is, unless people DO buy it, I won't be eating or paying my bills in the future.
So perhaps as an artist whose work would be just gotten for free by everyone who just doesn't feel like paying me for it, maybe I tend to see the other side of the coin more than those who are only facing the "do I get free stuff or not" point of view. But it is, nevertheless, very unjust to take for free what a person should rightfully and justly have to pay someone for.
There is very little in this world that is free. Yes, that's a harsh part of reality, but it is also a matter of justice. Nobody should be deprived of the benefit or gain due to them because of the work of their hands. And no Catholic should think that it is all right to deprive someone of just payment for their work, simply because some unscrupulous person has made it very easy to do so, or because they would simply rather not have to pay.
If we believe in justice, then there is something due or owed to a person for the work that they do. To deprive them of that in exchange for their work, for any reason (it's easy, everybody's doing it, I'm poor, etc.), is simply wrong. Injustice is still injustice, whatever the reasons or excuses.
In the case of scans... we're back to matters of law. Now if the law says, I may not take, distribute or copy a photo or scan that belongs to someone else (no matter what it's of), and it is not a sin for me to obey that law, then I am bound by Catholic morality to obey it. Even if it stinks, or even if the picture or scan is of someone's work who has been dead for hundreds of years. If the law says, "thou shalt not" then I am bound to obey it, so long as it doesn't contradict God's law.
Yes, people make some very stupid laws sometimes. But there is no danger to my soul if I go without a picture I like or wish I could have had. It IS a danger to my soul to break the law, even if I don't like that law. It is no sin to do without. It IS a sin to break the law.
To me, the matter of justice, and the requirement of Catholics to obey the law unless it contradicts God's laws, make the matter pretty clear. Obviously, the law varies from country to country, but... I think our Catholic conscience ought to tell us that if it's at all possible, we should pay for the work that we are trying to enjoy. And now that you can buy just about anything from just about anywhere, there is really no longer any excuse not to pay for it.
One example people used to cite was things like foreign video games, which other country's systems couldn't play. But by now, people can just order the system of the proper country on the internet. So basically, even these very uncommon objections no longer hold weight, since there is now a legal and moral way to be able to enjoy just about any work we want. Today, I can't think of virtually any instance in which it is actually impossible to pay the artist, if one really, really wanted to.