Accessing the image hash from within the container

Is is possible to access the hash-ID of the image used to create the container, from within the container? I want to provide a ‘signature version’ at the bottom of each page served from a php app running in a container.

I guess one way is to use Environment Variables from within the docker compose file:

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  • environment:
          - IMAGE_HASH=${IMAGE_HASH}
    

    and then have a wrapper script first of all write the IMAGE_HASH=ABC123 to a .env file before running docker-compose up. The script can inspect the image to get the hash ID.

    But I wonder if there is a ‘proper’ way to do this? So from within the compose file something like:

    environment:
        - IMAGE_HASH=this.imagehash
    

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