.gems

sinatra
rmagick

application.rb

require 'rubygems'
require 'sinatra'
require 'RMagick'

#How to use Sinatra, RMagick on Heroku

get '/' do
   content_type 'image/gif'
   img = Magick::Image.new(200, 200)

   gc = Magick::Draw.new
   gc.gravity = Magick::CenterGravity
   gc.pointsize = 32
   gc.font_family = "Helvetica"
   gc.font_weight = Magick::BoldWeight
   gc.stroke = 'none'
   gc.annotate(img, 0, 0, 0, 0, "Hello world!")

   img.format = "GIF"
   img.to_blob
end

config.ru

require 'application'

run Sinatra::Application