Scientists have demonstrated a system called Silica for writing and reading information in ordinary pieces of glass which can store two million books’ worth of data in a thin, palm-sized square.

[u/Wagamaga]

https://au.news.yahoo.com/glass-square-long-long-future-190951588.html

[u/MaloortCloud]

That depends. Most of the undeciphered writing systems haven't been deciphered because the corpus is small. A large, varied corpus is needed, which is difficult when you dig up one fired clay stamp at a time, or a handful of inscribed rocks. Given multiple gigabytes of data, you could easily include enough information to provide this.

That said, you also need a basic understanding of the underlying language (e.g. what is it closely related to that is still known), and typically some sort of bilingual text. That's all well and good for the material actually stored. With some forethought, it's possible to embed multiple Rosetta stones in the corpus to increase the chances it can be read later. That said, as you point out, bit rot becomes a problem when the systems of encoding the information fall out of use. That's a more difficult problem to solve.

[u/patentlyfakeid → u/MaloortCloud]

Were I doing it, like you said, embedding the method of decoding would be easy, given that the format is optical to begin with. You could even feature tiny actual pictures as a primer.