Posted by: paragon | September 4, 2007

Blocking Google Image Search


Schools (typically) want to block pornographic, risque and just plain ‘sexy pictures’ from students browsing through BorderManager HTTP Proxy. Using products like SurfControl, you can block many, many URL’s, but there has been a long-standing issue with Google Image search being a way for kids to look at pictures which administrators want to block.

As an example, go to, type in a search term of Pamela Anderson (or insert your own test name/porn star/beauty queen), select Images, and then select Google Search. The results may be quite interesting, but it points out why some admins want to kill Googel Search.


OPTION 1 – Block All Google Images In this option, we take a sledgehammer approach by trying to block all Google Images. Note that when you submit a search for Google images, you are redirected to a URL starting with We can set up a Deny URL Access Rule to block any such URL by denying:


OPTION 2- Force Google SafeSearch First of all, Google turns on a moderate level for SafeSearch by default. This setting attempts to block mature content from an Images search, but does not affect regular web searches. If this option is acceptable to you, then you only need to prevent the users from changing the setting (which is shown below).

If you want to use Strict Filtering, which tries to block mature content in regular searches as well as Image searches, you have to change the setting in Google (I assume on each PC, and each browser) and then prevent users from changing the options. In my limited testing, I could have no filtering set in Internet Explorer, and strict filtering set in Firefox, on the same PC using the same HTTP proxy. The settings are simply stored as a cookie on the browser, with no cookie equating to a moderate SafeSearch (Google default).

There are some problems with trying to prevent ‘mature’ pictures using SafeSearch. Apparently only English users can use Google’s content filtering technology (and it may be that only US schools seem to be so hung up on blocking these images to start with). There is this little warning on the Google site:

“WARNING: The results you see with this feature may contain mature content. Google considers a number of factors when determining whether an image is relevant to your search request. Because these methods are not entirely foolproof, it’s possible some inappropriate pictures may be included among the images you see. (The mature content filter is only available from an English interface.)”

Once you have changed the Google preferences, you have to prevent your users from being able to change the settings from the browser. Here is where we can try to block access to the URL’s that are used to change the search preferences. Put in a deny rule with the following settings (taken from a post in the Novell Public Forums):


Note that this blocks all ability to change preferences, and when I tested, it also blocked me from turning my ‘no search policy’ back to ‘moderate search policy’. Also prevented changes to all other preferences. So be sure the browser is set appropriately before you lock things down. (I simply deleted the cookies on the browser, and SafeSearch was re-enabled for me).

A Note On Yahoo Images

Yahoo Images has a similar feature, both for image searching, and for SafeSearch. However, you have to have a Yahoo ID just to change the search preferences. Nevertheless, the same sort of technique should be usable to block image searching on Yahoo, or to prevent changes to the preferences.

Try these entries in a Deny URL rule to block access to Yahoo Image search entirely:


At this time, I don’t have sample URL’s to use to block changing preferences.


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