The smallest QR-Codes to my knowledge are 25x25 blocks and thus if I want to detect the QR-Code in an image the part containing it needs to be at least 25x25 pixels.

Is there a smaller alternative (with a library implementation in python)?

The code should be able to encode at least 8 Bit of information. No information encoding with different colors should be used, the code should only use black and white.