Quoted from vid1900:I'm not a trademark attorney, so I'm not sure what the legal test is.
The picture is clearly based on the William Rimmer painting from the 1800s, so maybe now it's in the public domain?
The original Rimmer sketch is definitely public domain, anyone can use it. But the painting that's the Swan Song logo appears to be an original creation for the company, however much it references the Rimmer painting, and would not be in the public domain.
Stu made references to licensing images, so I suppose he licensed that too? Just surprised that the license holders are allowing it to be used on a commercial pin, even sans Led Zeppelin name.