Google (Nasdaq: GOOG) and Microsoft (Nasdaq: MSFT) have introduced software that makes it harder for users to search for child abuse material online, the companies said in a joint announcement Monday.

New controls from Google and Microsoft include algorithms that block images, videos and paths to illegal content and a halting of auto-complete features on child abuse search terms, according to the statement. They’ll work with the crime agency and Internet Watch Foundation to take down peer-to-peer networks featuring images of child abuse.

Writing ahead of a British summit on Internet safety, Google’s executive chairman Eric Schmidt said his company has fine-tuned Google Search to clean up results for over 100,000 search terms. When users type in queries that may be related to child sexual abuse, they will find no results that link to illegal content.

“We will soon roll out these changes in more than 150 languages, so the impact will be truly global,” Schmidt wrote in the Daily Mail newspaper.

The restrictions are being launched in Britain and other English-speaking countries first. Similar changes are being brought out on Microsoft’s Bing search engine.

The two companies are sharing picture detection technology to identify child abuse photographs whenever they appear on their systems, and Google is also testing technology to identify and remove illegal videos.

Other measures include warnings shown at the top of Google search for more than 13,000 queries to make it clear that child abuse is illegal.

Schmidt acknowledged that no algorithm is perfect and Google cannot prevent pedophiles adding new images to the web.

Campaigners welcomed the move but doubted how much impact the changes would bring. Pedophiles tend to share images away from the public search engines, they say.

“They don’t go on to Google to search for images,” said Jim Gamble, the former chief of Britain’s Child Exploitation and Online Protection Center. “They go on to the dark corners of the Internet on peer-to-peer websites.”

Meanwhile, U.K. Prime Minister David Cameron plans to introduce laws forcing search engines’ cooperation should new efforts to curb child pornography online fail, he said in London on Monday.

The prime minister credited Google and Microsoft with making “significant progress” in helping prevent such content from proliferating, in a statement ahead of today’s meeting of Internet companies, the National Crime Agency and charities on curbing such abuses.

In July, Cameron detailed his mission to stop child pornography and better protect children from pedophiles by enlisting help from companies and the law-enforcement agency. Since then, U.K. Internet providers have been installing home filters so parents can help prevent their children from being targeted and the largest Wi-Fi networks have activated so-called family-friendly filters in public areas where children may access the Internet.

Cameron cited a 20 percent drop in Internet users searching for illegal content thanks to efforts by Cupertino, California- based Google. Cameron also unveiled a U.K.-U.S. task force to identify trans-Atlantic criminals and said the Internet Watch Foundation — an industry group that identifies and removes illegal content — will expand operations and recruit new analysts.

Individuals will still need to monitor images to help sort “innocent pictures of kids at bathtime and genuine abuse,” Google’s Schmidt said. “Once that is done – and we know the pictures are illegal – each image is given a unique digital fingerprint” so computers can track and delete them.