If a picture is oversampled by a factor of N in both x and y directions, the resulting subarray for each original pixel contains up to N2 log2L bits of information, where L is the number of grey levels in each element of the subarray. The original pixel needs to be recorded at only about 8 bits for human viewing so the subarray can carry additional information. For example, a terrain map can be coded to include the x-y coordinates, the terrain height, and a geological descriptor. We describe a simple binary code (L=2) in which each 10 by 10 subarray (N=10) has its weight (the number of ones) constrained to yield 9 decimal descriptors. The code is self-synchronous so that no elaborate positioning techniques are required to read out the data.
Robert A. Gonsalves,
"Coding For Machine Readable-Human Readable Pictures", Proc. SPIE 0149, Digital Image Processing II, (7 December 1978); doi: 10.1117/12.956664; https://doi.org/10.1117/12.956664