Sex offender John Henry Skillern was caught by Google when he sent explicit images using his Gmail account
Sex offender John Henry Skillern has been arrested and charged after Google allegedly detected explicit images in his Gmail account(Webster Police Department)

Google's automatic email scanning technology has tipped off authorities about a 41-year-old man in Texas who was allegedly distributing explicit images of children via his Gmail account.

According to police, John Henry Skillern, 41, used his Gmail account to send three explicit images of a female child to a friend, reported local Houston TV station KHOU Channel 11 News

Skillern is already a registered sex offender who was convicted of sexually assaulting an eight-year-old boy in 1994.

Google's automatic image scanner detected the images and Google tipped off the National Center for Missing and Exploited Children, which contacted the Houston Police. Skillern has now been arrested and charged with possession of and promoting child pornography. 

"He was trying to get around getting caught by keeping it inside his email. I can't see that information, I can't see that photo, but Google can," Detective David Nettles of the Houston Metro Internet Crimes Against Children Taskforce told the TV station.

"I really don't know how [Google does] their job, I'm just glad they do it."

Investigators were able to get a warrant based on Google's tip and said they found other explicit images and text messages stating his interest in children on other devices, including mobile phone videos of children that had visited the Denny's restaurant in Pasadena where he worked.

Although Google has been scanning users' emails for many years in order to serve up more targeted search results and ads, the company only recently publicly acknowledged this in April, when it updated its Terms of Service following a US judge ruling which stated that Google had not specifically notify users about what actions it takes.

The terms now state very clearly that Gmail users are consenting to the search giant scanning the content of their emails:

Our automated systems analyse your content (including emails) to provide you personally relevant product features, such as customised search results, tailored advertising, and spam and malware detection. This analysis occurs as the content is sent, received, and when it is stored.

Google has been working with law enforcement to fight online child sexual abuse since 2006, but the company has only hinted that it is scanning emails to find images.

In a blog post last year, Google Giving's director Jacqueline Fuller wrote: "Since 2008, we've used 'hashing' technology to tag known child sexual abuse images, allowing us to identify duplicate images which may exist elsewhere. Each offending image in effect gets a unique ID that our computers can recognize without humans having to view them again.

"Recently, we've started working to incorporate encrypted "fingerprints" of child sexual abuse images into a cross-industry database. This will enable companies, law enforcement and charities to better collaborate on detecting and removing these images, and to take action against the criminals."