index.js

var WHITE = 255;

var readimage = require("readimage");
var fs = require("fs");
var gm = require("gm");

var load = function (file, callback) {
  var buffer = fs.readFileSync(file);
  var stream = fs.createReadStream(file);

  gm(stream).identify(function (err, info) {
    if (err) {
      return callback(err);
    }
    readimage(buffer, function (err, image) {
      if (err) {
        throw err;
      }
      callback(err, info, image);
    });
  });
};

var getAlignment = function (depth) {
  if (depth === 8 || depth === 16) {
    return depth;
  } else if (depth === 24) {
    // 24-bits depth images have 32-bits points.
    return 32;
  } else {
    throw new Error("Unsupported image depth");
  }
};

var readPoint = function (buffer, offset, alignment) {
  if (alignment === 8) {
    return buffer.readUInt8(offset);
  } else if (alignment === 16) {
    return buffer.readUInt16BE(offset);
  } else if (alignment === 32) {
    return buffer.readUInt32BE(offset);
  } else {
    throw new Error("Invalid alignment: " + alignment);
  }
};

var process = function (info, image, callback) {
  var frame = image.frames[0];
  var alignment = getAlignment(info.depth),
    points = frame.data.length / (info.depth / alignment);
  var columns = points / info.size.width,
    rows = points / columns;
  var i, column, pointColor;
  var histogram = {};

  for (i = 0; i < frame.data.length; i += (alignment / 8)) {
    column = i % columns;
    pointColor = readPoint(frame.data, i, alignment);

    if (!histogram.hasOwnProperty(column)) {
      histogram[column] = 0;
    }
    if (pointColor != WHITE) {
      histogram[column] += 1;
    }
  }

  // TODO(seykron): graficar histogram
  console.log(histogram);
  console.log(
    "Points:", points,
    "; Cols:", columns,
    "; Rows:", rows,
    "; Total points:", frame.data.length, "(" + columns * rows + ")");
};

load("captcha_decoded.jpg", function (err, info, image) {
  if (err) {
    throw err;
  }
  process(info, image, function (err) {
    if (err) {
      throw err;
    }
  });
});

package.json

{
  "name": "captcha-break",
  "version": "1.0.0",
  "description": "captcha breaking POC",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "seykron",
  "license": "GPLv2",
  "dependencies": {
    "gm": "^1.18.1",
    "readimage": "^1.1.1"
  }
}