[nearbygoogler]

I don’t know, still seems feasible. High quality full page images can be printed at ~2500x3500 pixels per page [1] (random print shop from the internet, but representative AFAICS), and that’s just what printers recommend for human readable images, they can produce images easily to 1200 DPI.

In another example, take the Machine Identification Codes (MIC) tracing dots that basic home printers can produce [2], (I bet the publishing industry could do much better to produce a high density grid.)

These dots have a stated diameter of 0.1 mm, and on an 8”x10” area one could get a grid of 80x25.4x25.4x(1/0.1mm)x(1/0.1mm)= ~5.1M dots.(wikipedia claims larger spacing, but that must be the protocol, printing itself allows for highly precise positioning) And that’s just for one color. Use CMYK (you could imagine a sub-project to design a 8bit color based dot scheme) and compression, and even with ECC losses I can see a few MB of encoded source per page being possible. And writing that decoder would be a great exercise!

[1]: https://www.docucopies.com/image-resolution/

[2]: https://en.m.wikipedia.org/wiki/Machine_Identification_Code