Passing the UPC Code
When an item lacks an ISBN in the 020 field (DVDs and CDs only generally have UPCs in the 024 field) the cover image is very much hit or miss. Syndetics has been contacted, however, it appears that Sierra needs to "pass the UPC code” in order for this to work. This addition would be helpful.

The product team will review this idea for consideration for a future release.
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Grace Palmisano commented
Yes @Lloyd Chittenden! The last two digits of the UPC are cut off and if that truncated number matches an ISBN number then that's the image that appears (regardless of whether or not it's the correct item).
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Lloyd Chittenden commented
Because of this bug you occasionally actually get the wrong cover. It does send a number from the 024. It takes the 12 digit UPC and chops off the last 2 digits and sends a 10 digit number. Syndetics tries to match that with a 10 digit ISBN. Now and then it finds a match, but it is not for the thing you have, it will send a cover for something completely different.