We should all feel "guilty" so long as there are still child abuse images on the internet, the head of the NSPCC said.
Peter Wanless called for the removal of all such pictures but admitted it would be a "gargantuan task" said "every one of us should feel at least a little guilty" while the problem persists.
Last month, David Cameron told a child abuse summit that a joint specialist unit run by the National Crime Agency and listening post GCHQ will target the most prolific offenders who are using increasingly sophisticated techniques to hide their true identities and encrypt and share images online.
Writing in the Daily Mirror, Mr Wanless described the campaign against sexual abuse of children as "one of the biggest challenges facing society".
He said around four in five child abuse images feature a boy or girl under the age of 11 - including babies - and half of them show children being tortured or raped by an adult.
He wrote: "Any society that allows such an evil scenario to play out uninterrupted must surely be demeaned and every one of us should feel at least a little guilty while it persists.
"Most importantly, we must never forget that these are not just pictures.
"They are crime scenes and children have been abused to create them. There is also evidence that some - not all - of those found with images will have committed other sex offences against children."
He continued: "While the summit's glow of satisfaction has dimmed, we have to turn to the real and ongoing job in hand: cleansing the web of all child abuse images.
"That may sound like pie in the sky, that the web is too intricate and full of dark corners - countless billions of pages where criminals can hide all kinds of material. But we need a zero-tolerance stance.
"Do we want to blindly slide into a situation where, a few years down the line, there are endless pictures in existence and so many offenders viewing them that it becomes an almost acceptable part of the downside of life, like burglary or fraud?
Is that the kind of tainted legacy we want to pass on? It may take time to achieve but we have to commit now."
Mr Wanless said he did not expect "this gargantuan task to be achieved overnight" but added there was progress from the Internet Watch Foundation, which monitors websites displaying child abuse images.
"Now it has the funding to work pro-actively, instead of waiting for reports to come in, it has identified nearly 28,000 offending web pages - more than twice last year's total," he said.
"Cleaning up the web sounds daunting and has never been attempted before on such a grand scale. But we must make it work.
"In five years' time I do not want to be looking out on a landscape that is still scarred by this problem which damages so many vulnerable lives."