This is the format that is used in the OpenGL and Microsoft DirectX development environment. It is used to store bitmap images of user interface environments and textures. It allows you to store information in compressed and uncompressed forms. It is used for texturing game models and storing entire textural arrays to create games and 3D-software applications. DDS is used to develop the latest-generation video game consoles. It makes it possible to compress texture blocks 'on the fly', which increases performance when you run the application.
ICO is a file of this format usually contains a small image icons of different resolutions (16x16, 32x32, 64x64 pixels) and various color depths (16 colors, 32, 64, 128, 256, 16-bit, and so on). Used to display files and folders in the graphical user interface (GUI) operating systems. This format can be opened with the help of the program ACDSee.