Whether we like it or not there is a huge percentage of the internet users, who are into Porn. The fact is that most of us deny that we watch porn.
Another fact is that out of the large number of Porn users, only a very small fraction would consider child porn acceptable (That is a group of people who have some physiological disorder).

The fact that we have to understand , here is that the majority of the population using porn are level headed enough to understand that child porn is wrong and that there is a young being suffering at the other end.

This population would not mind to report a site having child porn content if they can remain anonymous.

A centralized system like "phishtank" should be started where people can report child porn, the target user of this would be the current porn users.
The reasoning behind this is that it is the porn user who has a higher chance of encountering a site with child porn than a normal internet user.

Once such a database is built, the browsers can be reprogrammed to completely deny access to sites on this list. (That is confirmed to be such sites by crowd sourcing like on phishtank). The DNS servers can also be programed to do that.

The key element here is that the target crowd for this would be porn watchers. If it can be made an integral toolbar on the anonymous browsing mode on different browsers called incognito, private browsing etc it can be very effective because, this mode is most commonly used for visiting porn sites.

If such a database comes into existence, forums etc where user could post such content will also keep more vigil and ensure that their pages are clean because if they get on this list it will be a total lose of traffic.

The browser companies also should be willing to accept to implement total denial to sites on this list.