Bart Kuijper

When displaying a post or comment with avatars enabled, WordPress will always check for the existence of a Gravatar. (Note: even the default avatars ‘mystery person’ and ‘blank’ are in fact Gravatars served from gravatar.com.) WordPress does this by sending an MD5 hash of every displayed post or comment author’s email address to gravatar.com. Even with many plugins that introduce locally stored default or user avatars, this check still happens. On top of that, some themes or plugins force (Gr)avatars to load even if the display of avatars is disabled completely in WordPress’ settings. If for whatever reason you do not wish for Gravatar to receive these requests (which some people have voiced GDPR concerns about), this plugin is for you.
The way it works is every time WordPress attempts to display an avatar, this plugin first checks if the image is about to be retrieved from gravatar.com. If it is, the URL is changed to the locally stored ‘mystery person’ image (included with this plugin). If the avatar has any other source, this plugin doesn’t interfere.
Gravatars are also removed from the Discussion page in Settings and replaced with the locally stored ‘mystery person’ image. Again, any non-Gravatar images are left alone.
Upon activation of this plugin, if a Gravatar is selected as the default avatar, that setting is changed to the locally stored ‘mystery person’ image. If any non-Gravatar avatar is selected, that setting isn’t changed.
Upon deactivation of this plugin, if the locally stored ‘mystery person’ image is selected as the default avatar, that setting is changed to the Gravatar logo. If any non-Gravatar avatar is selected, that setting isn’t changed.

Redirect Gravatar requests

All requests to load an avatar from gravatar.com are redirected to a local image, preventing Gravatar from potentially gathering data about your site  …

Redirect Gravatar requests vs One User Avatar | User Profile Picture