I want to write a hit counter script to keep track of hits on images on a website and the originating IPs. Impressions are upwards of hundreds of thousands per day, so the counters will be incremented many times a second. 
I'm looking for a simple, self-hosted method (php, python scripts, etc.). I was thinking of using MySQL to keep track of this, but I'm guessing there's a more efficient way. What are good methods of keeping counters?
You could take your webserver's Access log (Apache: access.log) and evaluate it time and again (cronjob) in case you do not need to have the data at hand at the exact moment in time when someone visits your site.
Usually, the access.log is generated anyway and contains the requested resource as well as time, date and the user's IP. This way you do not have to route all trafic through a php-script. Lean, mean counting machine.
How to write an efficient hit counter for websites