Windows icon file, containing one or more small raster images.
| 0x00000000 | 00000100 | ···· | reserved + type 1 (icon) |
An ICO bundles several sizes of the same icon so the OS can pick the right one; browsers also use it for favicons. The header is a zero reserved word followed by image type 1.
Have a file that might be ICO? Identify it with the File Type Identifier — it reads the magic number locally, nothing is uploaded. Or browse all formats.