Which command is employed to build an image from a Dockerfile?

The command used to build an image from a Dockerfile is "docker build." This command is essential in the Docker ecosystem as it takes the instructions defined in a Dockerfile and compiles them into a Docker image. When running this command, Docker reads the Dockerfile located in the specified context directory, processes each command in the file in order, and constructs the image accordingly.

Using "docker build," users have the opportunity to create custom images that encapsulate application code, libraries, dependencies, and configurations, facilitating the deployment and sharing of applications in a consistent environment. This command is central to the workflow of Docker, enabling users to automate the creation of images and implement best practices in development and production setups.

The other options do not relate to the functionality required for building an image from a Dockerfile. For instance, "docker create" is used for creating a new container from a specified image but does not handle image building itself. "Docker compile" is not a recognized command in Docker's suite of commands, and "docker form" does not pertain to any valid actions in Docker. Thus, the "docker build" command is the correct and appropriate choice for the task described.