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.
DNG is an open-source raster image format developed by Adobe Systems and an extension of the TIFF 6.0 cross-platform universal format. The name of the format is an abbreviation of Digital NeGative Specification. The novelty was announced by the developer in 2004 as a standard format for RAW files. It is large in size because it contains not only the main image of high quality, but also metadata, as well as several images for preview (lower quality and resolution). Digital photos in this format are stored in uncompressed form.