One, that's not a barcode. It's a serial number. One is an image while the other is text. Okay, that is really a po-tay-toe po-tah-toe difference but I am feeling nitpicky today.
Also why would anyone wonder what a digital watermark looked like? We already knew what Booxtream put into the Pottermore ebooks:
Curiously enough, the Booxtream digital watermark used in Pottermore seems to be entirely different. Pottermore doesn't use that embedded serial number on every page. Maybe the above example came from a fixed layout textbook?