Example implementations relate to custom operating system (OS) images. For example, booting a user device to a custom OS image includes presenting a user interface (UI) for creating a custom OS image for portable use, storing the custom OS image on a database for information technology (IT) management purposes, sending, based on a request, the custom OS image from the database to an secure external device, and authenticating, based on a policy, the custom OS image on the secure external device for use on a user device without an OS image or a hard drive disk (HDD).