class Gallery < ActiveRecord::Base
  belongs_to :category
  has_many :gallery_images, dependent: :destroy
  accepts_nested_attributes_for :gallery_images, allow_destroy: true
end

class GalleryImage < ActiveRecord::Base
  belongs_to :gallery
  belongs_to :gallery_category
end


class GalleryCategory < ActiveRecord::Base
  has_many :gallery_images
end

<% for image in @gallery.gallery_images %>
  <li><%= image_tag(image.photo.url(:gallery_flexslider)) %>
    <p class="flex-caption"></p>
  </li>
<% end %>

<p class="flex-caption"></p>

<% @gallery.gallery_images.each do |image| %>
  <li><%= image_tag(image.photo.url(:gallery_flexslider)) %>
    <p class="flex-caption"><%= image.gallery_category.name %></p>
  </li>
<% end %>

<% @gallery.gallery_images.each do |image| %>
          <li>
            <%= image_tag(image.photo.url(:gallery_flexslider)) %>
              <% image.gallery_categories.each do |c| %>
                <p class="flex-caption"><%= c.name %></p>
              <% end %>
            </li>
        <% end %>

#app/models/image.rb
Class Image < ActiveRecord::Base
    has_many :gallery_images
    has_many :galleries, through: :gallery_images
    has_one  :category, through: :gallery_images #-> I think
end

#app/models/gallery.rb
Class Gallery < ActiveRecord::Base
    has_many :gallery_images
    has_many :images, through: :gallery_images
end

#app/models/gallery_category.rb
Class GalleryImage < ActiveRecord::Base
   belongs_to :gallery
   belongs_to :image
   belongs_to :category
end

#app/models/gallery_category.rb
Class GalleryCategory < ActiveRecord::Base
   belongs_to :gallery
   has_many :gallery_images
end

images
id | image_info | created_at | updated_at

galleries
id | name | created_at | updated_at

gallery_images
image_id | gallery_id | category_id

gallery_categories
id | gallery_id | name | created_at | updated_at

gallery_images
id | gallery_id | image_id | type | created_at | updated_at