Google CEO Larry Page AP Even though a registered sex offender was recently arrested after Google tipped off authorities to alleged child pornography images in the man's Gmail, Google isn't searching your emails for other crimes, the company told Business Insider.

And it can't mistake an innocent photo for an illegal one. A Google spokesperson told us:

Sadly all Internet companies have to deal with child sexual abuse. It’s why Google actively removes illegal imagery from our services — including search and Gmail — and immediately reports abuse to NCMEC [The National Center for Missing & Exploited Children]. This evidence is regularly used to convict criminals.

Each child sexual abuse image is given a unique digital fingerprint which enables our systems to identify those pictures, including in Gmail.

It is important to remember that we only use this technology to identify child sexual abuse imagery, not other email content that could be associated with criminal activity (for example using email to plot a burglary).

To unpack that a little ...

Internet companies have worked with the The National Center for Missing & Exploited Children to create a database of child pornography pictures. Each one of those is given a unique numerical number like a fingerprint, known as a "hash" in the tech world. When Google scans Gmail or the web, it is looking for those fingerprints.

If Google finds one, it is legally obligated to report it, attorney Chris Hoofnagle, director of information privacy programs at the Berkeley Center for Law & Technology, told Business Insider.

But your photo of your cute baby splashing around in the tub wouldn't be in that database and wouldn't be tagged with a finger print. So emailing that to grandma wouldn't cause Gmail to report you to authorities.

Likewise, this kind of search technique can't be easily translated to other crimes. It's not the same as a keyword search looking for words like "murder," "killed," "stolen" or "bomb." Think how many times people use use those words innocently. "My sister really overcooked those carrots. It was murder eating them." And so on.

That said, it doesn't mean that Google can't change its mind and start searching your Gmail for other things, warns Hanni Fakhoury, a staff lawyer for privacy watchdog organization the Electronic Frontier Foundation.

"There's nothing in their privacy policy that precludes them from doing that. Nothing in the law precludes them for doing that, as long as the user consents," he told Business Insider.

In fact, Google's Terms of Service tell you that you must follow the law when using its services and warns you that it analyzes your email and other documents you upload to serve you ads and perform services like scanning for viruses.

It is similar to the terms of service for all internet providers.

That kind of leeway has led to strange decisions by other email providers, Fakhoury said, such as when Microsoft admitted earlier this year that it once searched a blogger's emails when it suspected an employee had leaked proprietary software to the blogger.

And, on a somewhat ironic note, a source close to Google tells us that the hash technology that Google, Facebook, and others use to scout out child pornography was developed by Microsoft.