If you have the capability to take apart a notebook and stick its guts behind a store-bought frame, then taht seems to be the way to make the best final product. At least "best" in terms of appealing to the people in this forum.

Starting with an older Mac notebook, you can get a decent screen, wifi and the software built into the OS would be enough to run your image slideshow. Using nothing but the picture screensaver you can have a very nice transitioning slideshow using that panning and zooming Ken Burns effect and easily add images to a shared folder. The other benefit of this otherwise stock system is you can set the energy saver to shut the machine down and turn it back on again at specific times. No need to keep it running during the night when you're asleep or during the day if you're not home. To have a more complicated schedule you'll need third-party software to set up multiple on/off periods.

Theonly reason I haven't done this already is because I haven't been able to find a machine at my sweet spot. $100. It's only going to get easier because the older machines are coming down in price all the time. I'd like to make one for my parents, so maybe I can put something together at the end of the summer and then hold it for Christmas for them.