glitch image by giving a URL

app.rb

require 'rubygems'
require 'base64'
require 'json'
require 'sinatra'
require 'erb'
require 'open-uri'
require 'filemagic/ext'

class App < Sinatra::Base
  set :haml, {:format => :html5}
  set :public_folder, "public"
  set :views, "app/views"

  get '/' do
    mime_type = "text/plain"
    img = nil
    unless params[:image_url].nil?
      img = open(params[:image_url])
      mime_type = img.mime_type
      img = img.read
      img = glitch(img)
    end
    content_type mime_type
    img
  end

  post '/base64' do
    img = nil
    unless params[:base64_image].nil?
      img = Base64.strict_decode64(params[:base64_image])
      img = glitch(img)
    end
    content_type "application/json"
    # support JPEG only
    { mime_type: "image/jpeg", base64_image: Base64.strict_encode64(img) }.to_json
  end

  helpers do
    def partial(page, options={})
      haml page, options.merge!(:layout => false)
    end
  end

  private
  def glitch(img)
    replaces = params[:replacement] || '1'
    replaces = replaces.split ','
    repeat = params[:glitch_times].to_i || 10
    repeat = 1 if repeat < 0 or repeat > 300
    repeat.to_i.times do
      img.sub! %r(#{replaces.join("|")}), rand(10).to_s
    end
    img
  end
end

App.run! if __FILE__ == $0

Gemfile

source 'http://rubygems.org'

gem 'sinatra'
gem 'haml'
gem 'therubyracer'
gem 'coffee-script'
gem 'sprockets', '>= 2.0'
gem 'thin'
gem 'ruby-filemagic'
gem 'unicorn'

group :development, :test do
  # Pretty printed test output
  gem 'turn', '>= 0.8.2', :require => false
  gem 'rspec', '>= 2.0.0.beta.22'
  gem 'rack-test'
  gem 'cucumber'
  gem 'cucumber-sinatra'
  gem 'capybara'
  gem 'database_cleaner'
end