Word of caution: an entire NAS may be a bit of overkill if it’s JUST to get pictures from one device to another. Also consider that, if you get a small, cheap one, you may be tempted to tinker around with what else it can do - which will quickly become frustrating (“If only I had invested a LITTLE more, look at all the shiny fancy things I could do with it!”). Yes, I speak from experience (Synology DS 720+).

Seconded. Ideally this would sync with any mobile devices because I am incapable of self-control and putting my phone where I can’t reach it. I might even (gasp) pay for the privilege.