YouTube Safety Mode is only managed through cookies rather than URL parameters. This is likely a decision made to stop people inadvertently having Safety Mode enabled by clicking on a random YouTube link. To force Safety Mode, proxies can directly manipulate the cookie headers of outgoing requests, for example on this Bluecoat article you can see the script ...


Google has a reporting tool for objectionable content, such as websites and images. If websites aren't correctly filtered, you can submit them here.


Use the Google Feedback tool as shown here and report to Google regarding the inoffensive image being filtered. I believe there is a mechanism on their side to check if an image is being filtered by SafeSearch.


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.

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