If not, get a transparent pillbox with compartments for every day of the week (you can also get them with separate compartments for morning / evening).
Then put it in a place that he will always see it (eg. kitchen table).
No need for an app, and it's easy to check if he already took his meds or not.
Apps or other things are kinda bad, because you can silence the alarm and then forget to take the meds, or he can accidentally take the meds twice.
If all the doses for the week are prepared ahead of time, these mistakes are not so easy to make.
Perhaps you can skip the "before" photo, but it may help to reduce double doses.
If the contrast is high and you can calibrate the app using photos of an empty pillbox somehow, it doesn't look imposible. On the other hand https://xkcd.com/1425/
* The app has an alarm (like a clock). You can configure the time, let's say 9am.
* When it rings, the app put a message in the screen "Time to take your medicine. Please pick the pillbox and take a photo".
If he doesn't take the photo, make the app sound and show the message again after 2 minutes. After a few tries, send a message to some relative that is the guardian.
It will need some calibration to recognize the pillbox.
* After the photo of the pillbox, show a message: "Great. Today is Monday. Open the Monday slot and take another photo".
Repeat if there is no photo, and send a message to the guardian after some time. I'm not sure if in case of failure it is better to go to the previos step or not.
* After the photo of the open pillbox, show a message: "Take your medicine and then and take another photo"
It will need some calibration to distinguish the pills and the empty slot.
* After the photo of the empty pillbox, show a message: "Close the pillbox and store it. Great. See you tomorrow."
Something like this will need a lot of testing and perhaps FDA approval, but it doesn't look impossible.
(Perhaps it is easier to start with contraceptives pills, that have younger users that are more use to apps and don't have memory problems.)
Another option would be to call him every time he needs to take his pills and talk him through it. If that works, where the reminder apps don't, you could gradually switch to having someone else, like a caregiver, call him.
Another possibility is he doesn't like taking the pills because of how they make him feel but he's afraid to tell anyone.
He can check off each day on the paper calendar after he takes his pills.
If his calendar gets out of sync with his pill box, it's easy to re-sync. There's no single database.
I assume that while he probably looks at his phone every day, he definitely looks at his fridge many times a day.
If you want to get really high tech, you could add a $20 Wyze came and hang it near his pill box so you can check up on him.
Pillbox with pills for every day of the week works better.
I would say use this in combination with a well labeled pill box would be a good solution.
When you set the calendar entry, set both the reminder and click the repeat to choose 'daily'
https://www.amazon.com/gp/product/B004BRXI2U/ref=ppx_yo_dt_b...
It's pill box combined with an alarm clock.