get instagram picture url from page of instagram.

gistfile1.rb

require 'rubygems'
require 'net/http'
require 'uri'
require 'json'

class ExpandUrl
  def self.expand_url(url)
    uri = url.kind_of?(URI) ? url : URI.parse(url)
    Net::HTTP.start(uri.host, uri.port) { |io|
      r = io.head(uri.path)
      r['Location'] || uri.to_s
    }
  end  
end

class Instagram
  def self.isInstagram?(url)
    if url =~ /http:\/\/instagr\.am\/.*/
      return true
    end
      
    begin
      url = ExpandUrl.expand_url(url)
      if url =~ /http:\/\/instagr\.am\/.*/
        return true
      end
    rescue
      return false
    end
    false
  end
  

  def self.imgsrc(url)
    if (!(url =~ /http:\/\/instagr\.am\/.*/))
      url = ExpandUrl.expand_url(url)
    end

    host = host = "api.instagram.com"
    page = "/oembed?url=" + url
    insta = JSON.parse(Net::HTTP.get(host, page))
    insta['url']
  end
end