Can bar codes theoretically be considered a type of digital memory? Bar codes act just like any other device that contains data that you can read from. Can bar codes thus be considered a type of computer memory?

I believe the principle is quite similar to the optical discs like CDs or DVDs.

They work just like an SD memory card but instead of a card reader we use barcode scanner to read the digital data stored in the bar code.

Can bar codes be useful in other types of applications instead of identifying products? Can barcodes or similar technology be used in computers?
There is no god-given definition of (read-only) digital memory. We can think of several reasons for a writing system to be considered digital:


Can be read by a computer.
Cannot be read by a human.
Has high density.
Designed for use by computers.


Barcodes satisfy the first two properties, but not the third one: their density is rather low. Nevertheless, both traditional barcodes and modern QR codes were designed to be read by machines, and this gives credence to your claim.