TumblrでAPIを使用して写真を取得するスクリプト。tumblrのapi_keyと、gemのthorライブラリが必要です。usageは、オプションなしでコマンドラインから起動すると表示されます。とりあえず雑なエラー処理を組み込んだので、完走はするはず（並列処理はしないので極端に遅いですが）。

tumblr_v2.rb

#!/usr/bin/env ruby
# coding: utf-8

require 'rubygems'
require 'open-uri'
require 'json'
require 'thor'

class Tumblr < Thor
  desc "get_photos [BASE_HOSTNAME] [API_KEY]", "Download all photos by selected base-hostname (api-key required)"
  def get_photos(base_hostname, api_key)
    #create folder (adhoc support custom-domain, recently)
    folder_name = base_hostname.gsub(/\./, "")
    Dir.mkdir(folder_name) unless FileTest.exist?(folder_name)

    #get posts count
    info_url = "http://api.tumblr.com/v2/blog/#{base_hostname}/info?api_key=#{api_key}"
    begin
      info_json_hash = JSON::parse(open(info_url).read)
    rescue
      raise "first access to api is fail. please retry a little bit of late."
    end
    
    # max count
    max_posts_count = info_json_hash["response"]["blog"]["posts"]


    #regexs (for support 1280) and (file extension name)
    regex_std = /.*\/(.+?)o1_75sq\.jpg/
    regex_ext = /(.*png$|.*jpg$)/

    image_url_set = []

    # extract photo urls
    0.step(max_posts_count, 20) do |paging_num|
      posts_url = "http://api.tumblr.com/v2/blog/#{base_hostname}/posts?type=photo&api_key=#{api_key}&offset=#{paging_num}"
      begin
        json_hash = JSON::parse(open(posts_url).read)
      rescue
        redo
        # I think that go infinity loop maybe low percent.
      end
      posts = json_hash["response"]["posts"]

      posts.each do |post|
        # hummmm?
        raw_url = post["photos"][0]["alt_sizes"][-1]["url"]
        
        # generate filename from raw_url if i can
        filename = $1 if regex_std =~ raw_url
        image_url = "http:\/\/#{base_hostname}\/#{post["type"]}\/1280\/#{post["id"]}\/1\/#{filename}"

        # set 500px's url when i can't get filename
        image_url = post["photos"][0]["alt_sizes"][0]["url"] if filename == nil
        image_url_set << image_url
      end
    end

    # download file to folder
    image_url_set.each do |image_url|
      local_filename = image_url.split(/\//).last
      local_filename += ".jpg" unless regex_ext =~ local_filename 
      File::open("#{folder_name}\/#{local_filename}", "wb") do |f|
        begin
          f.write(open(image_url).read)
        rescue
          p $!
        end
      end
    end
  end
end

Tumblr.start