Gravatar is bad in terms of data security and privacy.

• Gravatar analyses the way YOU navigate the internet.
• The most egregious part of Gravatar’s service is the inability to stop them from collecting your data.
• Trying to cancel a Gravatar registration is not allowed and they will continue to track your e-mail address for the rest of time.
• Gravatar does not provide any details about how they use your personal information and does not respond to any queries relating to privacy issues.
• Gravatar is not an opt-in service.
  • However, they will not display an avator unless you register, but if a site is Gravatar-enabled, every time visit it your information is sent to Gravatar.
  • Their Privacy Policy is silent on this point; and they have not responded to enquiries on this point.
  • They track your internet usage across different sites if the same e-mail address is used.

https://meta.stackexchange.com/questions/44717/is-gravatar-a-privacy-risk

https://en.wikipedia.org/wiki/Gravatar