Well, if the same picture can belong to an Event AND a biography at the same time, it gets kinda complicated, but if one picture can only belon to an event OR a biography, the simple solution is a polymorphoc association.
class Biography < ActiveRecord::Base has_many :pictures, :as => :image end
class event < ActiveRecord::Base has_manny :pictures, :as => :image end
class Picture < ActiveRecord::Base belongs_to :image, :polymorphic => true end
Now your Picture Model only needs 2 special fields:
image_id (Integer) = the foreign key of the object it belongs_to image_type (string) = the Class Name of the object it belongs_to
those 2 fields are handled by ActiveRecord, you dont have to provide the values yourself ...
now you can do:
@event.pictures # get all Pictures of an event ... OR ... @event = Event.pictures.build(someParaamsHere) @event.save ... ETC .. and all the other stuff you could do with a simple has_many <-> belongs_to relationship.
Read more here: http://wiki.rubyonrails.org/rails/pages/PolymorphicAssociations
Theres also a way for polymorphic habtm relationships, and an example
in the wiki, but i didnt fully understand it yet 
