Previous to WordPress having post thumbnails built in, there was a script called TimThumb. I know quite a few themes that integrated TimThumb in order to automatically generate post thumbnails instead of relying on the old method of using a custom field. Ben Gillbanks has chronicled the short history of TimThumb.
Development was started by Tim (hence the name) one of the programmers at Category4 where Darren worked. Shortly after the release of Mimbo Pro, with Tims blessing, we decided to open source the code releasing TimThumb on Google code, and that’s when everyone else started using it. Nowadays 95% of the premium themes teams are offering TimThumb support – and it’s a great feeling, knowing so many are making use of code I worked on.
The article was published in 2009 but I was fooled because I saw it as a recent submission on WPVote.com. Still worthy of a good read though.