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.
MNG is an image file category format. It supports all possible PNG and JPEG compression algorithms (including gamma correction and translucency) in order to create animated images. It was available in the Mozilla browser from 2000 to 2003. Now supported by Konqueror browser. MNG, i.e. Multiple-image Network Graphics, has the closest connection with PNG. In 1995, when they started developing the PNG format, it was decided not to include animation support. For a simple reason: then this feature was used infrequently. And yet, we started working on MNG, that is, the version of PNG that supports animation. The initial version of the MNG specification was born in early 2001. The MNG format is a simplified raster analogue of Adobe Flash. Each frame has many layers, and they can be moved relative to each other, scaled, cropped. This explains the complexity of supporting the MNG format. As a result, the MNG file structure resembles the PNG structure. The only difference is the identification tag. And also that much more options of blocks (chunk) are applied. MNG frames are saved as PNG or JNG. Compared to GIF, this format supports animation. Compared to JPEG, it provides the smallest file size due to compression loss. Compared to PNG, compression is done without distortion. Now MNG is not supported by popular browsers and software, since it was replaced by a simpler APNG format.