Currently, a link to Google and its logo are displayed in the language/en/help_bbcode.php file to explain how to correctly format tags and to add an image to a post. However, the Google logo is outdated and Google does not allow the use of its logo on third-party websites. Plus, that overload their servers. I used the blue phpBB logo to replace it because the grey one with transparent background is hardly visible.
Originally, I just refreshed the old Google logo with the new one (https://www.google.com/images/srpr/logo5w.png) but Joas proposed to use the phpBB logo, and I agree with him.