- validates :width, :presence => true, :numericality => true, :natural_number => true
- validates :height, :presence => true, :numericality => true, :natural_number => true
- validates :visible, :presence => true, :numericality => true, :inclusion => {:in => 0..3}
+ validates :visible, :presence => true, :numericality => true, :inclusion => {:in => 0..1}
+ validates :author_id, :presence => true, :numericality => true, :existence => {:both => false}