The daily price of bitcoin has a clear on-chain signal.
The open source program UTXOracle.py extracts this price
using 100% on-chain data (no exchanges or third parties).

Update - Starting in November 2023, very small transactions
began to overwhelm the on chain round USD transactions used
by UTXOracle, leading to confusion.

We're currently working on an update with a better mechanism
while for filtering out non-round USD transactions.