I'm not sure where you are encountering the most violations, but Ebay users will face new restrictions on the use of watermarks. If Ebay enforces their new rules adequately, placing a watermark will force Ebay sellers away from using your images.

I agree, though, that watermarks tend to interfere too much with the information that is being conveyed - an accurate depiction of a chip.

As for a copyright notice, there is debate in the legal community whether a new copyright can be claimed for a straight-up scan of an item in which the original designer owns a copyright. The creator of an original work owns a copyright (by operation of law), but a scan or photo without any original contribution added may lack the originality required. If you decide to use a disclaimer such as that shown, you may wish to consider "Image source: Museum of Gaming History" (or something similar - maybe including the website address to generate traffic) rather than a copyright notice.