File with an .ICO extension contains a small image – two bitmaps; used as an icon of programs and catalogues in Windows system. The two bitmaps, one called „AND”, imaging a mask indicating transparency and the other one – „XOR”, containing icon image.

An example of frequently used ICO file is favicon.ico, a 16 x 16 pixel icon which is a logo of an Internet website, which is loaded in the website’s address bar, if it is present in the main catalogue on a server of the page. ICO format is similar to a different type of file used to display a cursor in Windows – CUR. Utilising additional software, appearance of icons can be edited.