In November 2009, Google began allowing you to set your browser to a permanent (cookie specific) SafeSearch lock for your images search results. So if you never want adult related images to show up in Google Images, you would set that computer to be locked on SafeSearch.
But last Friday the feature stopped working. A Google Web Search Help thread has reports of the lock, well, not locking. Users trying to lock the SafeSearch filter found themselves back to not being on SafeSearch when using Google Images.
Google admitted to the issue yesterday and reportedly fixed it. 'TomBee' from Google said:
There have been some problems with this feature in the last couple of days. I have just tried it and seems to be working now. Sorry for any inconvenience!
For more details on locking SafeSearch, see this document.
Forum discussion at Google Web Search Help.