First, you need to create a use in www.gravatar.com. go to www.gravatar.com & signup. Follow the instruction step by step shown on this post.
And then fill the form on fig 2
Please enter your email that you want use on wordpress or already your using on wordpress.
After create a account, than you must verify account using your email. Please check your inbox and click Activate Account link.
How to login
After login, please give authorize to use your profile picture in wordpress shown on fig 4
After login to account. Setup the profile picture.
And choose picture from computer or any link below shown in fig 5
If you select picture from your own computer please flow the next step in fig 6
After selecting a picture than choose a gravatar ranking shown on fig 7
Now go to Profile and do the 4 steps shown on fig 8
And fill the form shown on fig 9
That’s all. Now you can show your own profile picture in wordpress post & comments using this email address.