Symptom
After deleting a person's entry in Address Book, the picture associated with that entry continues to appear in Mail.
Solution
First, locate the picture you wish to remove.
Address Book stores pictures in the folder:
Note: The tilde character (~) represents your Home directory. Click the Home icon in the Finder toolbar, then proceed to your Library folder and so on.
After you navigate to the People folder, you see files with names that correspond to the email addresses in your Address book. The files carry the filename suffix ".tiff." An example could look like:
To remove the picture from Mail, simply drag it to the Trash.