Hi, everyone, and welcome to this lecture. In this lecture, I'm going to explain what images are and what they're used for. An image provides the base operating environment for applications to run on a Compute instance. You can use images to archive application versions for disaster recovery, and even to roll back an instance. After registering an image, the image can be used to create one or more exact replicas of the original disk. You can use operating system images to create boot disks for Compute instances. 

There are two types of images available. They include public images and custom images. Public images are provided and maintained by Google, open-source communities, and even some other third-party vendors. All GCP projects have access to public images so they can be used to create instances. There are many pre-configured public images available in Compute Engine that have compatible Linux operating systems and Windows operating systems. These systems images can be used to create and start instances.

When you use an image, Compute Engine will create a persistent boot disk for each instance that you spin up, using your chosen image. By default, the boot disk that is created will be the same size as the image that was used. In situations where you need a persistent boot disk that's larger than the image used, you can always resize the boot disk later. While most public images are available at no additional cost, some premium images will result in additional costs to your instances. 

Custom images are available only to your project. Custom images can be created from boot disks and even from other images. After creating a custom image, you can use it to create an instance. You can use a custom image to import a boot disk image from an on-prem machine into Compute Engine. You can also use custom images to import virtual disks from existing virtual machines that are running in your environment. A custom image that's imported into Compute Engine will not add any additional cost to your instances. However, it will incur an image storage charge, as long as you keep the custom image in your project.