simple gravatar / avatar image module, alternative to https://gist.github.com/1339702

avatarable.rb

module Avatarable
  extend ActiveSupport::Concern

  GRAVATAR_IMAGE_BASE_URL     = 'http://www.gravatar.com/avatar/'
  GRAVATAR_IMAGE_DEFAULT_SIZE = '32'
  DEFAULT_URL                 = 'http://your-awesome-domain.com/images/your-awesome-default-image.png'

  # Avatarable assumes the class (or other module) that includes this module has an email attribute
  # if the email attribute is named something other than email, use alias_attribute to map it to email
  # alias_attribute :email, :your_email_attribute

  module ClassMethods
  end

  module InstanceMethods
    # return the default url, use when you want to just return the default image
    # without checking for an email / gravatar
    def default_avatar_url
      DEFAULT_URL
    end

    # if no email value, returns the default avatar url
    # otherwise returns the generated gravatar_url
    # options include:
    #   size    => size of image to display, can be within the range "1" to "512"
    #              defaults to "32" if not specified.
    #              TODO: handle resizing of default avatar. as is, assumes the
    #              default size and / or passed option size will match default avatar
    #              imagess size. Could implement http://domain.com/images/avatar_{size}.png
    #   default => default image to display if no gravatar is found
    #              defaults to default avatar if not specified.
    def avatar_url(options = {})
      options[:default] ||= DEFAULT_URL
      options[:size]    ||= GRAVATAR_IMAGE_DEFAULT_SIZE
      if email.blank?
        options[:default]
      else
        gravatar_url(options[:size], options[:default])
      end
    end

    private

    # return the gravatar image url for the specified email
    # specify image size and default url if no image is found
    def gravatar_url(size, default)
      "#{GRAVATAR_IMAGE_BASE_URL}#{gravatar_email_hash}?s=#{size}&d=#{CGI.escape(default)}"
    end

    # generate the gravatar image based on their specifications:
    #   1. Trim leading and trailing whitespace from an email address
    #   2. Force all characters to lower-case
    #   3. md5 hash the final string
    # via: http://en.gravatar.com/site/implement/hash/
    def gravatar_email_hash
      Digest::MD5.hexdigest(email.strip.downcase).to_s
    end
  end
end

sample usage:

model:

def Comment < ActiveRecord::Base
  include Avatarable
end

view:
- unless comment.anonymous? = image_tag comment.avatar_url - else = image_tag comment.default_avatar_url