Analysis of information sources in references of the Wikipedia article "ICO (file format)" in English language version.
Icons have a maximum size of 256x256 pixels, making them suitable for high-dpi (dots per inch) displays. These high-resolution icons allow for high visual quality in list views with large icons... Only a 32-bit copy of the 256x256 pixel image should be included, and only the 256x256 pixel image should be compressed to keep the file size down.
The cursor is loaded properly at whatever color depth the cursor was authored. However, the system cannot distinguish between multiple candidates in the same cursor file or resource that differ only by their color depths. Icons, however, fully support multiple icon candidates with varying color depths.
See the second comment.We use "image/x-icon" because that's the MIME type we've always used. Someone at some point (AFAIK, not related to Microsoft) proposed registration of the MIME type as "vnd.microsoft.icon", but Windows doesn't actually use that, it uses image/x-icon.
The cursor is loaded properly at whatever color depth the cursor was authored. However, the system cannot distinguish between multiple candidates in the same cursor file or resource that differ only by their color depths. Icons, however, fully support multiple icon candidates with varying color depths.
