Google just can't win. I beat up Google on showing pornography or inappropriate images in their image search engine or on web search way too often. We complained in December that Google Image Search was too sensitive and then Google seemed to have relaxed the filter in June. But then we saw more porn or images that would upset some people.
Now, I am seeing reports at WebmasterWorld that Google may have tightened the filter to be more sensitive again. The filter does not appear to be as strong as the December filter, but it is discussed that it is more strict that after the June changes.
This is a hard balance to find but it is something Google and other image search engines struggle with daily.
Forum discussion at WebmasterWorld.