As of April 2015, there is no official Instagram app for computers running Windows 8. However, users are able to install unofficial programs for interacting with the Instagram interface, such as Instagram HD, or use the program BlueStacks, to install the Instagram Android app on the computer.
BlueStacks is a special developer environment program that simulates the Android smart phone operating system on a Windows computer. By installing this program, users are able to simulate the Android operating system environment within the Windows machine and run any Android apps on the computer, such as Instagram. Alternately, Instagram does offer a web interface that allows users to comment on and like photos, though it doesn't support an upload feature.