A web page showing a child being sexually abused is identified by a watchdog every eight minutes - with some victims younger than two years old.
The stark figure was revealed by the Internet Watch Foundation, which marks its 20th anniversary on Friday, having identified and removed more than a quarter of a million URLs since it was launched.
IWF chief executive Susie Hargreaves said: " What's truly shocking is not always the numbers of reports to our hotline, but what is shown in those images and videos.
"Each and every one of those quarter of a million reports is the record of the sexual abuse of a child. These are real children. The majority are under 10 years old. Some are younger than two."
She said the IWF has seen a huge rise in the number of images that are available and shared.
"The reality is that people can access these images everywhere," Ms Hargreaves added. "They don't have to go out of their house.
"Images are created every day. No-one knows exactly how many are out there."
The IWF received its first report at 11.21am on October 21 1996, by telephone. Twenty years on, its analysts have assessed a total of 699,403 reports, with 281,781 positively identified as containing illegal child sexual abuse imagery.
A report might show just one or thousands of images or videos of sexual abuse.
In addition to the quarter of a million web pages, the IWF has also logged 125,000 "digital fingerprints", known as hashes, which are a unique code generated from the data in an image.
Experts have compiled a database of individual codes of known images of child sexual abuse in order to tackle the issue of duplicated material.
The IWF has teamed up with Microsoft to create a system that will allow internet companies around the world to use the hash list to stop the upload, sharing and storage of abuse images.
Ms Hargreaves described the step as a "major breakthrough".
She said: "Every eight minutes our analysts identify a new web page showing a child being sexually abused. We always ensure that image is taken down.
"But in the past it could be uploaded again and again. This was incredibly frustrating for us and dreadfully sad for those victims.
"Now our new technology allows us, and any company which uses the image hash list, to hunt out those abusive images, meaning internet companies can completely stamp out copies, stop the sharing, and even stop the image being uploaded in the first place."
When it was founded, the IWF said 18% of the world's known child sex abuse imagery was hosted in the UK - a figure that now stands at 0.2%.
Ms Hargreaves said: "We feel that's a testament to the work of our analysts."
The parents of murdered April Jones voiced their support for the IWF's work.
The five-year-old's killer, Mark Bridger, was found to have accessed child abuse images online before her death.
April's father, Paul Jones, said: " The more of this (child sexual abuse imagery online) you can remove, take away, it's going to be the better so potential paedophiles haven't got the chance to see these images and then move on to the next stage."