I expect the site owner took the photos themselves. I assuming copyright would even apply to the appearance of most cassette tapes, why would the copyright holders sue, what would they expect to gain? The web site itself could likely use a fair use defense, maybe not the T-shirt business.

They're more likely to have trademark issues with the T-shirt business. A consumer might reasonably assume a t-shirt with an image of a Sony cassette tape on it was made by Sony. Maybe they were careful in their selection of which tapes are on t-shirts on their own, the links to the actual store (on a German site) don't work for me.