function isICNS (buffer) {
  return ('icns' === buffer.toString('ascii', 0, 4));
}
Image Entry

| Offset | Size | Purpose                                                          |
| 0	    | 4    | Icon type, see OSType below.                                     |
| 4      | 4    | Length of data, in bytes (including type and length), msb first. |
| 8      | n    | Icon data                                                        |