I get that the grandmother side of thing is “old school” because of the printed photos, but why is the “modern” input side of this also using antiquated tech like sms?
IMO this is actually a really good decision given the purpose of the service. A lot of my older family members that I will likely invite to my new account (great idea btw) are familiar with sending pictures through SMS and don't really use any other messaging apps or many apps at all, if their phone even supports apps. Believe it or not many older people and some younger people still rock low powered phones with little or no data plan. However most if not all phones made within the last decade can send SMS messages and more than likely are on a plan with free texting.
Why should I need to download another app that is a glorified REST client when SMS does the job perfectly well?
They may be familiar with sending images over MMS, which generally limits the size to less than half a MB. Hardly "high quality".
I never once suggested that it should be an "app". This could literally be a web page with a single file input and a button, or a fucking customer-specific email address. It could be any number of things that makes more sense than sending shit quality images over MMS.
My father has an email account solely because an Android phone makes you get one. He definitely doesn't know the password and I wouldn't be surprised if he didn't know the address either. However he is very comfortable taking pictures and attaching them to text messages.
He can easily save a contact in his phone on his own. I or my brothers would have to help him set up a bookmark in a browser. Now my father may be somewhat of a Luddite but keeping the barrier really low for family members who aren't texh savvy is a good idea for this.
And as far as quality I can almost guarantee my grandma doesn't care what is in the pictures or how blurry they are. She is going to care that I am sending her something. That's the important part not HD images.