prueba de concepto de app

app.rb

require 'sinatra'
require 'rest-client'
require 'json'

API_KEY = "satan"

#Asumiendo que existe un cliente que llama este endpoint así:
#$.post("myapp.heroku.com/image", {image: base64ified_image }).done(function(data){ console.log(data.image_url)})
#hostealo aquí
#https://devcenter.heroku.com/articles/rack


post '/image' do
  raw_response_from_imgur = RestClient.post(
    "http://imgur.com/api/upload.json", 
    key: API_KEY,
    image: params["image"]
  )
  response_from_imgur = JSON.parse(raw_response_from_imgur.body)
  content_type :json
  {image_url: response_from_imgur["link"]}.to_json
end

Gemfile

gem 'sinatra'
gem 'rest-client'
gem 'json' #probablemente innecesaria