Totally open, public image bucket

I'm an artist trying to create a public use printer that can be connected to via QR code from anywhere. A person uploads an image and the bucket is scanned via cron job on an Raspberry Pi connected to an on site printer, The cron job tells the priunter to print the image.

I want this to be a seemless setup, no accounts, no passwords, just scan and drop the image. I'm guessing this would not be the default experience and I need to find a way around users needing account credentials.