Francesco Vannini has written a tutorial, based on work by Andrew Mulholland, to allow you to use a Raspberry Pi Zero as a mass storage device which can be read as a source by a digital picture frame. Read it here. It’s an interesting method and use for the USB capabilities of the Zero and Francesco also covers his mistakes and wrong turns along the way.
Did I misread this? It sounds like once it is displaying as a usb stick you cannot change the contents. If true, it’s pretty worthless!
I think he just did it as an experiment with the hope that someone would be able to do something a bit more sophisticated.
Awesome! Take a look at http://dakboard.com for the software side of things. It makes creating a digital picture frame extremely easy with the Raspberry Pi!