There’s supposed to be an option, right…
Maybe the ‘ground plane’ is hiding them…
Shadows on, hides picture, shadows off shows picture.
Shadow ‘intensity’ adjustment causes permanent glitch.
Maybe there’s a deficiency between ‘shadow plane’ and picture frame elevation…
Turning off ‘show underside’ helped mitigate this.
If there was a way to have a transparent ground plane or something, that would be great 
It makes no sense that ‘turn off ground plane’ would mean that the shadows should be off too.
You should still be able to have shadows.
I was able to further mitigate this bug, by using viewport settings instead of application settings:
It’s odd that the ‘automatic altitude’ here still uses the custom altitude parameter – but I’m glad it does.