According to @BitMEXResearch, they constructed a Bitcoin (BTC) transaction with a single 15-of-15 P2SH multisig input and one output, measuring 1.69 KB in size (source: @BitMEXResearch on X, Aug 26, 2025). The post states that 14 of the 15 private keys are intentionally vulnerable and can be calculated from on-chain data, and those 14 keys together encode a 439-byte JPG image (source: @BitMEXResearch on X, Aug 26, 2025). This on-chain demonstration highlights concrete key-derivation risk and data-embedding behavior that traders can factor into BTC custody, wallet infrastructure choices, and chain analytics monitoring (source: @BitMEXResearch on X, Aug 26, 2025).