All you need to do is say that you got the image from the ChipGuide. Read below.

ChipGuide Usage Policy

The Museum of Gaming History has been granted use of the images shown on the ChipGuide by their owners. In some cases, the ChipGuide has modified these images to meet its guidelines. The Museum of Gaming History retains its rights over the image modifications.

All content (descriptions, webpages, etc.) other than images, on the ChipGuide is copyrighted and use of any of the contents requires expressed written consent, with these exceptions:

1) Images and descriptions (but not entire webpages) may be used for non-commercial purposes, such as educational purposes or trade lists, if the source is identified as "The Museum of Gaming History's ChipGuide".
2) Commercial use includes, but is not limited to, sales, auctions and publications.
3) ChipGuide Numbers (CGxxxxx) may be used to identify items cataloged on the ChipGuide for both personal and commercial use. ChipGuide numbers can be used in publications (including websites) if the source is identified as "The Museum of Gaming History's ChipGuide".
4) Use of ChipGuide website content is hereby granted to the Casino Chip and Gaming Token Collector's Club (CC&GTCC), The Museum of Gaming History in any and all of their endeavors, including Casino Chip and Token News and their websites.