For a lot of things, VLMs are good enough already to provide rewards. Give them the recent images and a text description of the task and ask whether the task was accomplished or not.
For a more general system, you can annotate videos with text descriptions of all the tasks that have been accomplished and when, then train a reward model on those to later RL against.
For a more general system, you can annotate videos with text descriptions of all the tasks that have been accomplished and when, then train a reward model on those to later RL against.