How get correct path default image using gem dragonfly?

I use for loading files gem dragonfly

I have model Photo:

class Photo < ApplicationRecord
    dragonfly_accessor :avatar do
      default  'public/avatar.png'    
    end
................................
end

When i call pry(#<#<Class:0x007f83508fb8f0>>)> @photo.avatar.url

I get

=> "/media/W1siZmYiLCJwdWJsaWMvYXZhdGFyLnBuZyJdXQ/avatar.png?sha=338938a0ea07d56b"

Setting file dragonfly.

dragonfly.rb

require 'dragonfly'

# Configure
Dragonfly.app.configure do
  plugin :imagemagick

  secret "7c510e8ed95f9929f09981ef5f42ffc75034703184575044d2835ebbbd2a350b"

  url_format "/media/:job/:name"

  datastore :file,
    root_path: Rails.root.join('public/system/dragonfly', Rails.env),
    server_root: Rails.root.join('public')
end

# Logger
Dragonfly.logger = Rails.logger

# Mount as middleware
Rails.application.middleware.use Dragonfly::Middleware

# Add model functionality
if defined?(ActiveRecord::Base)
  ActiveRecord::Base.extend Dragonfly::Model
  ActiveRecord::Base.extend Dragonfly::Model::Validations
end

I need path image for paste in image_tag. How can I get correct path .../public/avatar.png?

I founded solution:

dragonfly_accessor :avatar do
      default  Rails.root.join('public', 'images', 'default', 'avatar.png')    
    end