If you save digital data (ASCII) on an analog form like a cassette tape is that okay? Seems you could alternativly put metallic strips in a book. What about QR Codes? Could you have a massive QR Code on each page which contains a section of source code? Could you use an alternative encoding like dots and lines (.||.||....|.|.|..|) to represent 1s and 0s which is easy to scan (and not require OCR/checksums)?
To what extent does analog encoding fall under the illegal threshold?