Image has a lot of creator owned content but sometimes it can evolve from that to a long running series like Spawn and Savage Dragon the former which had a tv adaption,a movie adaption,video games,and merchandise ,while the latter got a cartoon series in the 90's.
Here are the list of Image long runners
Spawn: Around since 1992 one of the two image launch titles still being published.
Savage Dragon:Around since 1992 one of the two image launch titles still being published.
Youngblood: Started in 1992 it had most issues and relaunches.
Cyberforce: One of the first top cow titles had a lot of mini-series and spin-offs.
Witchblade: lasted from 1995 to 2015 with a few spin-offs and a relaunch from 2017-2019.
Darkness: Lasted from 1996 to 2015 with a relaunch in 2019.
The Walking Dead: laster from 2003 to 2019
Invincible: lasted from 2003 to 2018.
Saga: Will last up to 108 issues.
Well that is all the long runners I can find what do you guys think?