Something that made me wonder with numismatic articles... how do they have many images yet I don't see much references. Krause is a prime example. Do they mainly own the coins / banknotes or have permission? Or they purchase them for business and sell them at a later date? It may be a compilation from various collectors but I don't recall seeing a long list of authors or references...
I suspect mainly it's that they have permission, or are interpreting the clause in copyright law "for educational purposes" as giving them permission. I think the BCCS journal for example might have blanket permission to reproduce Heritage and PCGS images in articles, although they are frequently thanked for them at the end of articles too. I agree that more often than not images in these publications are not credited.
We collectors tend to buy & sell our coins routinely. I now own a seated quarter that has a recognized die variety that PCGS has imaged on their website. They had the image long before I had the coin.
I believe that many collectors are happy to see their coin published but do not wish to have their name used.