capt.rb

#!/usr/bin/env ruby
require 'rubygems'
require 'RMagick'

captcha = "9277f49ecee"
#10.times { captcha << (rand(26)+65).chr }

canvas = Magick::Image.new(1280,800, Magick::HatchFill.new('#ffffff','#4169e1'))

text = Magick::Draw.new
text.annotate(canvas,0,0,0,0,captcha) {
        self.fill = "#000000"
        self.stroke = "transparent"
        self.pointsize = 72
        self.font_weight = Magick::BoldWeight
        self.gravity = Magick::CenterGravity
}
canvas = canvas.swirl(30)
canvas = canvas.implode(-0.45)
data = canvas.to_blob { self.format = "jpg" }
puts data

ruby capt.rb > image.jpg