function getExifThumbnail(dataView, offset, length) {
    if (!length) return
    if (offset + length > dataView.byteLength) {
      console.log('Invalid Exif data: Invalid thumbnail data.')
      return
    }
    return new Blob(
      [loadImage.bufferSlice.call(dataView.buffer, offset, offset + length)],
      {
        type: 'image/jpeg'
      }
    )
  }
Returns the Exif Thumbnail data as Blob.

@param {DataView} dataView Data view interface
@param {number} offset Thumbnail data offset
@param {number} length Thumbnail data length
@returns {undefined|Blob} Returns the Thumbnail Blob or undefined