Azure Compute Gallery is a service that helps you build structure and organization around your custom VM images.Azure Compute Gallery provides three main value propositions:

* Simple management

* Scale your custom images

* Share your images - share your images to different users, service principals, or AD groups within your organization as well as different regions using the multi-region replication

A managed image is a copy of either a full VM (including any attached data disks) or just the OS disk, depending on how you create the image. When you create a VM from the image, a copy of the VHDs in the image are used to create the disks for the new VM. The managed image remains in storage and can be used over and over again to create new VMs.

If you have a large number of managed images that you need to maintain and would like to make them available throughout your company, you can use a Azure Compute Gallery as a repository that makes it easy to update and share your images. The charges for using a Azure Compute Gallery are just the costs for the storage used by the images, plus any network egress costs for replicating images from the source region to the published regions.