Google 's email account.
John Henry Skillern, from Houston, was eventually arrested by authorities for possession and distribution of abusive content. The man was apparently attempting to send three images of child pornography via his email.
The illegal material was detected by Gmail's automated image scanning system. When Google noticed the photos, it contacted the National Center for Missing & Exploited Children, reporting the incident. Skillern was found to be a known sex offender, so police immediately arrested the perpetrator after issuing a warrant.
The fact that Google scans users' emails should come as no surprise. The company doesn't hide this fact, and its terms of service clearly state the process by which the company's automated systems analyze the content of emails in order to display more targeted ads.
The question remains, however, whether Google has the right to contact the authorities regarding illegal material found in e-mail accounts, and how the company determined the nature of the specific images.

