def get_iiif_image_url(iiif_manifest):
    """Given a IIIF manifest dictionary, derives the value for the info.json
    file URL, which can then be stored in the roll metadata and eventually
    used to display the roll image in a viewer such as OpenSeadragon."""

    resource_id = iiif_manifest["sequences"][0]["canvases"][0]["images"][0]["resource"][
        "@id"
    ]
    return resource_id.replace("full/full/0/default.jpg", "info.json")