After re-reading: you avoid prosecution by not being a large enough offender, or by offending in a jurisdiction where law enforcement is not trained to catch you. Not all that different than avoiding prosecution as a recreational drug user when the cops are too busy going after bigger fish.
There's a lot of time and resources spent in between the time of identifying that an IP address is broadcasting CP to having all the information you need to bust down the right door and lock up the guy for a long time.
Taking your example of image analysis, companies in this space will build applications that - for instance - identify which images of the 10,000 on a bandit's computer are all the same kid. The software company would use sample images of clothed kids to demonstrate how it works, then only law enforcement would input confiscated CP images to do the analysis.
I meant how do you avoid prosecution when analyzing these images for the purpose of catching the people spreading them? There is no "fair use" for contraband. Therefore, it would be hard to build a company around technology for stopping child pornography.
There's a lot of time and resources spent in between the time of identifying that an IP address is broadcasting CP to having all the information you need to bust down the right door and lock up the guy for a long time.