'Lookup the images for the given URIs
Backends can use this to return image URIs for any URI they know about
be it tracks, albums, playlists. The lookup result is a dictionary
mapping the provided URIs to lists of images.
Unknown URIs or URIs the corresponding backend couldn\'t find anything
for will simply return an empty list for that URI.
:param uris: list of URIs to find images for
:type uris: list of string
:rtype: {uri: tuple of :class:`mopidy.models.Image`}
.. versionadded:: 1.0'

def get_images(self, uris):

    validation.check_uris(uris)
    futures = {backend: backend.library.get_images(backend_uris) for (backend, backend_uris) in self._get_backends_to_uris(uris).items() if backend_uris}
    results = {uri: tuple() for uri in uris}
    for (backend, future) in futures.items():
        with _backend_error_handling(backend):
            if (future.get() is None):
                continue
            validation.check_instance(future.get(), collections.Mapping)
            for (uri, images) in future.get().items():
                if (uri not in uris):
                    raise exceptions.ValidationError((u'Got    unknown    image    URI:    %s' % uri))
                validation.check_instances(images, models.Image)
                results[uri] += tuple(images)
    return results
