Not particularly useful, but fun! The cashu people are back with an easy way to stash ecash in a PNG image.

The page asks a Cashu mint (Minibits) for a Lightning invoice. Once it’s paid, the mint signs tokens without seeing them, using blind signatures. Together they make a cashuB token: a few hundred bytes of signed proofs that whoever holds them can spend.

Hidden in the lowest bits

The token is written into the last bit of every red, green and blue value, pixel by pixel in row order. Each colour moves by at most 1 out of 255. A 1280 × 960 photo has room for about 460 KB; a token needs about 1 KB.

I like the idea of making this an option for all cashu wallets: you tap the send button and then there's an extra little option to send tokens as image. If it was standard and all cashu wallets could also decode, it would be a pretty fun form factor.