By default, Adobe's Photoshop image-editing program does not support ICO format, making it impossible to make an ICO file in Photoshop on a Mac computer with the default configuration.

Icons use the ICO file extension, but due to file formatting issues, it won't work to simply change the file extension of a JPEG file to ICO.

An icon file is a format in which icons of various sizes are stored in ".ico" file which is one extension, and the background is transparent.