A few major changes:

[selectricity] / app / models / candidate.rb

class Candidate < ActiveRecord::Base
  belongs_to :election
  validates_uniqueness_of :name
  validates_presence_of :name

  def <=>(other)
    self.name <=> other.name 
  end
  
  def to_s
    name
  end

  def picture=(picture_field)
    if picture_field
      unless picture_field.content_type.match(/^image/)
        return false
      end
      self.picture_filename = base_part_of(picture_field.original_filename)
      self.picture_type =  picture_field.content_type.chomp
      self.picture_data = picture_field.read
    end
  end

  def base_part_of(filename)
    name = File.basename(filename)
    name.gsub(/[^\w._-]/, '')
  end

  def picture?
    !self.picture_filename.nil?
  end

end