Hi,
When you upload an image, an entry in the database is made for the image. It links the image with the product using is product_id.
You have uploaded some images which are not linked to a product. So the "file_ref_id" is 0.
It could happen when you upload an image during a product creation and you removed the image before saving this new product.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.