gistfile1.rb

#http://blog.wyeworks.com/2009/7/13/paperclip-file-rename

 Paperclip.interpolates :default_image_type do |attachment, style|
    attachment.instance.get_user_default_profile_image
  end
  
  Paperclip.interpolates :normalized_avatar_file_name do |attachment, style|
    attachment.instance.normalized_avatar_file_name
  end
  
	# store User avatar
	has_attached_file :avatar, :styles => {
			:hero => '20x20',    # To show on top header with user name
			:small => '45x45',   # To show with activity
			:thumb => '110x110'  # To show on User profile page, or on thumbnails.
		},
		:default_url => "/images/:default_image_type_:style.png",  # default image for an user. TODO: Change it as per user sex (m|f)
		:url => "/system/avatars/:id/:style/:normalized_avatar_file_name",
    :path => ":rails_root/public/system/avatars/:id/:style/:normalized_avatar_file_name"

  validates_attachment_size :avatar, :less_than=>500.kilobyte
  validates_attachment_content_type :avatar, :content_type=>['image/jpeg', 'image/png', 'image/gif']
  
  def normalized_avatar_file_name
    return transliterate(self.avatar_file_name)
  end
  
  def transliterate(str)
    # Based on permalink_fu by Rick Olsen
  
    # Escape str by transliterating to UTF-8 with Iconv
    s = Iconv.iconv('ascii//ignore//translit', 'utf-8', str).to_s
  
    # Downcase string
    s.downcase!
  
    # Remove apostrophes so isn't changes to isnt
    s.gsub!(/'/, '')
    
    # Replace any non-letter or non-number character with a space
    s.gsub!(/[^A-Za-z0-9_\.]+/, ' ')
  
    s.strip!    
  
    # Replace groups of spaces with single hyphen
    s.gsub!(/\ +/, '-')
  
    return s
  end


 #Paperclip Custom Interpolations to pick default user on his/her sex
  def get_user_default_profile_image
    default_image_type = 'm'
    if self.avatar_file_name.blank? # Means no file uploaded yet
      if !self.sex.blank? and self.sex.upcase == SEX_TYPE[:female].upcase
        default_image_type = 'f'
      end
    end
    return default_image_type
  end