code: function getJpegSize(imgData) {
  
      var width, height, numcomponents; // Verify we have a valid jpeg header 0xff,0xd8,0xff,0xe0,?,?,'J','F','I','F',0x00
  
      if (getImageFileTypeByImageData(imgData) !== 'JPEG') {
        throw new Error('getJpegSize requires a binary string jpeg file');
      }
  
      var blockLength = imgData.charCodeAt(4) * 256 + imgData.charCodeAt(5);
      var i = 4,
          len = imgData.length;
  
      while (i < len) {
        i += blockLength;
  
        if (imgData.charCodeAt(i) !== 0xff) {
          throw new Error('getJpegSize could not find the size of the image');
        }
  
        if (imgData.charCodeAt(i + 1) === 0xc0 || //(SOF) Huffman  - Baseline DCT
        imgData.charCodeAt(i + 1) === 0xc1 || //(SOF) Huffman  - Extended sequential DCT
        imgData.charCodeAt(i + 1) === 0xc2 || // Progressive DCT (SOF2)
        imgData.charCodeAt(i + 1) === 0xc3 || // Spatial (sequential) lossless (SOF3)
        imgData.charCodeAt(i + 1) === 0xc4 || // Differential sequential DCT (SOF5)
        imgData.charCodeAt(i + 1) === 0xc5 || // Differential progressive DCT (SOF6)
        imgData.charCodeAt(i + 1) === 0xc6 || // Differential spatial (SOF7)
        imgData.charCodeAt(i + 1) === 0xc7) {
          height = imgData.charCodeAt(i + 5) * 256 + imgData.charCodeAt(i + 6);
          width = imgData.charCodeAt(i + 7) * 256 + imgData.charCodeAt(i + 8);
          numcomponents = imgData.charCodeAt(i + 9);
          return [width, height, numcomponents];
        } else {
          i += 2;
          blockLength = imgData.charCodeAt(i) * 256 + imgData.charCodeAt(i + 1);
        }
      }
    }
docs: JPEG SUPPORT
   takes a string imgData containing the raw bytes of a jpeg image and returns [width, height] Algorithm from: http://www.64lines.com/jpeg-width-height