Below is a totally made up example.
So let's say on the left we have a weird black-white image or, in other words, a matrix of zeros and ones. We then apply a specific algorithm to the given matrix. The result is shown on the right - it is still represented by a pretty weird image but this time a circle can be visually distinguishable in our outcome.
The idea is that the circle (or any other simple figure for that matter) was planned to appear there all along. Yet that same figure was not visually obvious to be there in the beginning.
How could I realistically recreate a similar result? Maybe some have seen sources referring to like-minded ideas? Essentially I'd need a simple model which relies on underlying patterns that are not (easily) visually distinguishable.
I am aware that visual cryptography is almost synonymous with having multiple layers which when properly combined reveal the result. I'd love to go with a single layer even if it is not safe in terms of hiding information. I was thinking about functions and subtle algorithms (such as cellular automata) which potentially could be used in order to recalculate every element of a matrix but no luck so far.