App to use iMac as digital photo frame for photos on a network drive?

Question 1

I’d like to use a spare iMac as a digital photo frame to display my personal photos.

Desired features:

Turn off screen when the room is dark (or, worst case, turn off based on a timer — would the Energy Saver schedule be sufficient for this?)
Access photos from a shared network drive (so it automatically gets new photos) — this Mac will not actually contain a local copy of any of the pictures
Randomize order of photos
If possible, allow multiple monitors (with different photos on each)
Doesn’t need any fancy animation effects — I’d prefer it being more like a static picture that doesn’t change that often, just like a traditional photo on the wall

Are there any apps you’d recommend that can meet these needs (especially accessing photos from the shared network drive)?

Question 2

Nobody volunteered a solution, so here’s what I did…

Screensaver: I used the in-built screensaver, with a few changes (see below)
The Default duration of the slide show was too quick (3 seconds), so I used OS X Mavericks screensaver changes pictures too quickly: How do I slow it down? to fix it. Note the special csrutil instructions since Yosemite.
Network drive: I mounted a network drive, then changed the Login Options to permanently mount it. See: How to Automatically Connect to a Network Drive at Login in OS X
On/Off control: I used the Energy Saver control panel to Wake & Sleep the machine at set times. Not as good as sensing light/motion, but it will do for now.

Answer