What Is Gravatar?
An “avatar” is an image that represents you online—a little picture that appears next to your name when you interact with websites.A Gravatar is a Globally Recognized Avatar. You upload it and create your profile just once, and then when you participate in any Gravatar-enabled site, your Gravatar image will automatically follow you there.
Understanding how to get images from Gravatar
When you sign up in gravatar, you need to register an unique e-mail. Gravatar uses that email address to generate an unique MD5.hexdigest key, and then, it links that key to your image file.
Let’s take a look at my gravatar image url:
Parameter after the avatar is the MD5.hexdigest key generated with your email, let’s try generate that in our application and check if it gives the same result:
require "digest/md5" Digest::MD5.hexdigest('firstname.lastname@example.org').to_s
Result is “1c7b91342323ab699f6668f3317ed1bb”
So now you can write your own tool to get the gravatar user image: just use the email to generate the key and append it to the url.
If you are looking for more options while fetching the image you can use gems like gravtastic which lets you get images of different sizes, avatar rating and different filetype.