As you might imagine, this is something that's come up in the past. It would definitely be possible to write a script that hits the openframe API to accomplish this, but I'm not aware of anyone that's done it.
Since the API stores a record for each individual Artwork and each Artwork needs to have a web-accessible URL (nothing is stored on the Openframe servers), the way I'd imagine this working is that the script would loop through the photos (e.g.) in a directory and create an Artwork via the API for each of the desired files.
Another option would be to create an "format extension" that expects a URL to a web directory and can handle all of the logic for displaying whatever is in the directory. E.g. you might be able to create an "photo-directory" extension that expects a URL to a directory of photos and then manages looping through them on some interval. The extension could use
fim, which is an cli image viewer that has some built-in slideshow functionality. (An earlier version of the openframe-image extension used fim).