Files that contain the .ico file extension are image container files that store icons that are used by different Windows applications, such as the Windows folder icons, file icons and program icons that appear on a user's desktop.
The ICO file is not an image file itself. It is a container file that stores two bitmaps and the image mask that is used to create the icon that is saved in the file. ICO files can be modified to create custom icons for a Windows interface and are sometimes downloaded with Windows desktop themes.
ICO files are similar to CUR files, but they have a different identification byte in the file header.
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