On November 11th, 2009, Google introduced the ability for users with Google Accounts to lock on the SafeSearch level in Google's web and image searches. Once configured, a password is required to change the setting.[1]
On December 12, 2012, Google removed the option to turn off the filter entirely, requiring users to enter more specific search queries to access adult content.[3][4][5]
SafeSearch can be enforced by local area network administrators and ISPs by adding a DNS record. This is often done on school networks to prevent students from accessing pornographic content.[6][7]
Users themselves can turn this setting on to filter out any inappropriate content.[8]