File type: Icon
ICO files are special image files that are used for icons in the windows operating system for various applications, shortcuts, folders and files.
These files have two bitmaps within them - AND bitmap which indicates the image mask and determines which part of the icon should be transparent; and XOR bitmap which contains the image of the icon, which is then mapped over the image's mask. These files can be modified in most graphical editing software applications such as Adobe Photoshop to create new custom icons which can be associated to different files or folders.
On web servers ICO files do not have much use except one very specific uses for a single icon file namely favicon.ico. This file is yet another icon file similar to the one described above but bears special meaning for the web server. It is generally placed in the root directory of the web server or the web application and needs to be mapped in the files of the web application by mapping a link to it in the header of the html files.
On doing so this icon will then appear on the user's browsers as an image representing the web site. Modern browsers such as the Internet Explorer 6.0 and above and Firefox show the icons of the web sites along with the title of the web sites.