function isSegmentStart(dataView, offset) {
    return (
      dataView.getUint32(offset) === 0x3842494d && // Photoshop segment start
      dataView.getUint16(offset + 4) === 0x0404 // IPTC segment start
    )
  }
Tests if field segment starts at offset.

@param {DataView} dataView Data view interface
@param {number} offset Segment offset
@returns {boolean} True if '8BIM<EOT><EOT>' exists at offset