It also seems to me (not a Rabbi btw) that it’s really just a feeling of what is Shabbos’dik. If you would sit down and look at paper photo albums on Shabbos, there shouldn’t be much difference ‘looking’ at an electric photo album. Obviously [since anybody might be reading] that means you’re not touching the thing or pushing any buttons.
I’m sure it takes a bit getting used to. And if you’re trying to teach a toddler about Shabbos, it might be confusing. The first time we left the frame on, my 3-y/o nephew asked if he could watch TV or play the computer (can’t remember which). That may have been because someone left the computer on accidentally also in another room, but I think the frame contributed cuz he was watching it a lot.
So i think you just have to be clear about its use. I wouldn’t invite friends and family over to watch a slideshow and would avoid putting any videoclips/music on it. And maybe keep it on a timer so it’s not an all-day attraction. Also, I would slow down the transitions so it’s less like a ‘show’ and more just a nice background thing. So you might look at it one moment and think that was a nice trip back in 1984, but you wouldn’t just stare at it all day if it takes 30 seconds to a minute plus for the next picture to appear.