ICO is a format (full name - Icon File) of bitmap images and refers to system files. Developed by Microsoft and designed to store icons in its operating system. ICO files, as a rule, store icon images - modest in size, with a small resolution (from 16x16 to 64x64 pixels), with different color depths (from 16 colors). In the graphical interface of various operating systems, ICO format files are used to display files, programs and folders (primarily in Windows) or as an icon for a specific website.
JPEG is the most common and popular bitmap format. The form got its name from the name of the organization-developer Joint Photographic Experts Group. Files of this format are used today in all digital cameras and cameras. They have a good compression ratio and support 24-bit color depth. Since such compression significantly reduces image size with virtually no loss of quality, JPEG format is widespread on the Internet. However, the stronger the compression, the worse the quality. In addition, the JPEG format does not support the transparency option.