Operation Magenta saw officers from 34 police forces carry out simultaneous raids on 75 addresses across the country.
The Abusive Images Unit of Greater Manchester Police (GMP) and the Child Protection and Investigation Unit of the Hertfordshire Constabulary drove the six-month investigation.
A Manchester Police spokeswoman said the raid "shows that the Internet is not unpoliceable and those who both attempt and succeed in obtaining these images will be targeted by police".
The police used a software tool developed by SurfControl to track and trace illegal and threatening activity in Internet chat rooms. Steve Purdham, SurfControl chief executive, said specialist software now meant it was "impossible for those who use the Internet illegally to remain anonymous".