User agents, IP addresses, and browsers loading javascript are all methods I've heard of to measure whether an impression is a real person. Is there a checklist, good guide for lessons learned, or a toolkit out there you would recommend?
Just a suggestion: If you want to post the same question again, don't post the same question. Ask what you really want, and explain why existing tools don't meet your needs. Make it clear that you've investigated existing offerings, and share your findings.
Is there a reason you cannot just outsource this problem to AWstats/Webalizer/Google Analytics/etc? It's a hard problem, and those packages have done quite a bit of work to solve it.<p>(From experience, switching from - IIRC - AWstats to Webalizer reduces your traffic by a lot, as the latter's robot detection algorithm catches more robots. IIRC - it's possible that it's the other way round...)`