evodata/app/helpers/users_helper.rb

module UsersHelper
  def user_gravatar(user, options = {})
    options = {alt: "avatar", class: "avatar", size: 80}.merge! options
    id = Digest::MD5.hexdigest(user.email.strip.downcase)
    url = "http://www.gravatar.com/avatar/" + id + ".jpg?s=" + options[:size].to_s
    options.delete :size

    image_tag(url, options)
  end
end