In Google Image Search, it's possible to report individual offensive images. How can I report web pages (or entire websites) that contain offensive images? These pages occasionally show up in search results, even with SafeSearch enabled.
Google has a reporting tool for objectionable content, such as websites and images. If websites aren't correctly filtered, you can submit them here.
What I can suggest is to use the Google Feedback tool and report the image not being properly filtered by SafeSearch. I have the steps in this question.