FIRST

This actually isn't the best solution. It seems like all of this logic
should instead be the concern of some sort of Photo model, which may or
may not need be an association. With that being said, here's my take...

page.rb

# Your Page model
class Page < ActiveRecord::Base
  # Create a callback to delete the photo file if appropriate.
  # This is nice because in the case where the page is otherwise
  # invalid, it won't unnecessarily delete the photo
  after_save :delete_photo_file, :if => :photo_deleted?
  
  # Setter method that gets called when you pass :clear_photo => true
  # to update_attributes
  def clear_photo=(clearing)
    if has_photo?
      @deleted_photo_path = photo_file_name
    end
  end
  
  # Check for presence of deleted photo path. If set, then we can assume
  # that the photo has in fact been deleted
  def photo_deleted?
    @deleted_photo_path
  end
  
  # Check for the presence of a photo_file_name. If set, then we can assume
  # that the page has a photo.
  def has_photo?
    photo_file_name
  end
  
  private
  
  # Callback method invoked by the after_save
  def delete_photo_file
    File.delete("#{RAILS_ROOT}/public/images/frontend/#{photo_file_name}")
    self.photo_file_name = nil
    save!
  end
end

pages_controller.rb

# Your controller action:
class PagesController < ApplicationController
  def update
    # First, find the appropriate page...
    @page = Page.find(params[:id])
    
    # Update the attributes
    @page.update_attributes!(params[:page])
    
    # return some sort of response
  end
end

routes.rb

# Add this to your routes:
map.resources :pages

view.html.erb

<%= link_to_remote "Delete this image", page_path(@page, :page => { :clear_photo => true }), :method => :put) %>