In regard to pixel labeling, I’ve also seen sensor_msgs/Image used as a means to publish, along with some custom structure to define the mapping between pixel values and labels on a separate topic. It would be cool to also have a message type to publish a array of convex bounding polygon verticies with label IDs. That’s a common use case when labeling regions of an image, and would be good compressed representation to transmit instead for classification modalities that utilise that format.