Files with the extension ICO contain icons, ie Small graphics that represent the representation of files or directories in a graphical user interface (GUI). They are used by different operating systems, eg Microsoft Windows.
The graphics can be in different resolutions and color depths. The most common are 16x16, 32x32 and 64x64 pixels. Color depths from 16 colors (4 bits) to true colors (24 bits) are possible.
In addition to the normal graphics programs that can handle ICO, there are also special software that is designed to edit and create icons.
Most often resolving problems with opening ICO files is very simple. Just install an appropriate program that supports such files. All of the listed programs support ICO files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of ICO files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate ICO files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Apple Preview applications is not on the list, select "Browse" option in order to manually locate the directory where Apple Preview has been installed.
Sometimes problems with opening ICO files may not lie with the application itself, but can arise due to other causes, such as: