barcode/qr-code/RFID sticker (to identify the product) & set of cheap(ish) wireless weighing scales could probably do it easier than trying to estimate based on

barcode/qr-code/RFID sticker (to identify the product) & set of cheap(ish) wireless weighing scales could probably do it easier than trying to estimate based on crappy phone pics. Does require more infrastructure though, but might not be a huge deal for the stockroom if it improves the workflow/reliability of stock levels.