Twitter#update_with_media(status, OpenURI.open)

twitter-gem-and-open-uri.rb

require 'twitter'
require 'open-uri'

config = YAML.load_file('twitter.yml')
Twitter.configure do |c|
  c.consumer_key = config['consumer_key']
  c.consumer_secret = config['consumer_secret']
  c.oauth_token = config['oauth_token']
  c.oauth_token_secret = config['oauth_token_secret']
end

# Tempfile
begin
  uri = URI.parse('https://dev.twitter.com/sites/default/files/images_terms/tweet-display-guidelines-20110405.png')
  media = uri.open
  media.instance_eval("def original_filename; '#{File.basename(uri.path)}'; end")
  p Twitter.update_with_media(Time.now.to_s, media)
rescue => e
  p e
end

# StringIO
begin
  uri = URI.parse('http://a3.twimg.com/a/1315421129/images/logos/twitter_newbird_blue.png')
  media = uri.open
  media.instance_eval("def original_filename; '#{File.basename(uri.path)}'; end")
  p Twitter.update_with_media(Time.now.to_s, media)
rescue => e
  p e
end