Google is not consistant with its URL presentation between the different search options. The first time you search in a brand new google window you get a URL such as "http://www.google.co.uk/search?hl=en&q=hello&meta="
Repeat searches in that google window doing a normal google search the search results URL includes a reference to the filtering option eg
"http://www.google.co.uk/search?gbv=2&hl=en&safe=active&q=hello&btnG=Search&meta= "
Where you can see safe=active refearing to the search type. This is not the case when you do a google image search. In addition there is no way to enfore the use of strict filtering, as both strict and moderate have the same url format.
To be fair google's interesting and varied implimentation of how to make reference to the selected filtering option in the URL make it difficult to filter correctly.
J