Aha so it also serves as proof that work is being done by the miner?
So the 'F':s in the middle also guarantees that it holds no bitcoin value?
When a bitcoin miner is at work, it tries many nonces x, such that sha256(sha256(block_header_with_nonce(x))) results in a number that is small enough.
Currently, this number needs to be smaller than
(written in hex) for it to result in a real bitcoin block with value. Pools, however, (at least the ones i know about), only request hashes that are smaller than
So, it will see all "real" hashes calculated by the miner, but also many hashes that are somewhat larger than this.
The pool gets its income from those real hashes calculated by the miners, and distributes them (using some formula)
according to the number of low-difficulty hashes it received from each miner.