Set your Gravatar account image to your Address Book entry on your Mac.

gravatar.plist

<!-- Copyright (c) 2012 David Heaney -->

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>KeepAlive</key>
        <false/>
        <key>Label</key>
        <string>com.dejay.gravatarmac</string>
        <key>ProgramArguments</key>
        <array>
                <string>/usr/local/bin/gravatar</string>
                <string><%= email %></string>
        </array>
        <key>RunAtLoad</key>
        <true/>
</dict>
</plist>

gravatar.rb

#!/usr/local/bin/macruby

# Copyright (c) 2012 - 2014 David Heaney

require 'digest/md5'
require 'net/http'

framework "ScriptingBridge"

name     = ENV['USER']
book     = SBApplication.applicationWithBundleIdentifier("com.apple.addressbook")
download = "/Library/Caches/Gravatar/#{name}/#{name}.png"

begin; Dir.mkdir("/Library/Caches/Gravatar/#{name}"); rescue

Net::HTTP.start("gravatar.com/") do |http|
    resp = http.get("/avatar/#{Digest::MD5.hexdigest(ARGV.first.downcase)}")
    open(download, "wb") do |file|
        file.write(resp.body)
    end
end

data = NSImage.alloc.initWithContentsOfFile(download)
book.myCard.setImage(data)

Rakefile

# Copyright (c) 2012 David Heaney

require 'erb'

UNAME = ENV['USER']
AGENT = "/Users/#{UNAME}/Library/LaunchAgents/com.dejay.gravatar-mac.plist"

desc "Install Gravatar-Mac!"
task :install do
  puts "Please enter the email that you wish to use for Gravatar-Mac:"
  email = STDIN.gets.chomp
  system "sudo cp bin/gravatar /usr/local/bin/gravatar"
  system "sudo chmod +x /usr/local/bin/gravatar"
  
  plist = "com.dejay.gravatarmac.plist"
  agent_dir = File.expand_path("~/Library/LaunchAgents/")
  agent = File.join(agent_dir, plist)
  Dir.mkdir(agent_dir) unless File.exists?(agent_dir)
  File.open(agent, "w") do |f|
    f.puts ERB.new(IO.read(plist)).result(binding)
  end 
  puts "Done!"
end

desc "Uninstall Gravatar-Mac (BOOO!)"
task :uninstall do
  system "sudo rm /usr/local/bin/gravatar"
  system "rm /Users/#{UNAME}/Library/LaunchAgents/com.dejay.gravatar-mac.plist"
  puts "Done!"
end