function isICO (buffer) {
  var type;
  if (buffer.readUInt16LE(0) !== 0) {
    return false;
  }
  type = buffer.readUInt16LE(2);
  return type === TYPE_ICON;
}
Image Entry

| Offset | Size | Purpose                                                                                          |
| 0	    | 1    | Image width in pixels. Can be any number between 0 and 255. Value 0 means width is 256 pixels.   |
| 1      | 1    | Image height in pixels. Can be any number between 0 and 255. Value 0 means height is 256 pixels. |
| 2      | 1    | Number of colors in the color palette. Should be 0 if the image does not use a color palette.    |
| 3      | 1    | Reserved. Should be 0.                                                                           |
| 4      | 2    | ICO format: Color planes. Should be 0 or 1.                                                      |
|        |      | CUR format: The horizontal coordinates of the hotspot in number of pixels from the left.         |
| 6      | 2    | ICO format: Bits per pixel.                                                                      |
|        |      | CUR format: The vertical coordinates of the hotspot in number of pixels from the top.            |
| 8      | 4    | The size of the image's data in bytes                                                            |
| 12     | 4    | The offset of BMP or PNG data from the beginning of the ICO/CUR file                             |