Bitcoin miners have the aim to check the transactions made and after this to add groups of transactions to the block chain. As every user share is hardware to work for the same cause but the mining done by every system is not equal, so share is prize by the bitcoin mining pool to the clients who present a valid proof of work.
From different types of approaches an interesting one is 'Meta-hash' technique, used by puddinpop's (remote miner). Miner of bitcoin mining pool generates hashes, and also passes on Meta-hashes; these are hashes of large lumps of generated hashes. Network server checks that the meta-hashes are real or fake; bitcoin mining pool picks up a meta-hash from each miner that hasn't been checked on the longest. At the end this prevent miner in the pool from simply claiming rewards.
These approaches are made to make safe the interest of each and every user of bitcoin mining pool against foreclose unsporting by the clients and the server.