My client want to make sure that his marketers meet some of their specific clients on a regular basis. I had thought of that this could be possible by getting the clients fingerprints. But as I read in several pages, the fingerprint api is available in android api 23+ and in Samsung devices it is not possible to check the fingerprints of people other than the phone owner.
Is there any alternatives that one can use for physical authentication (not like password)?
I want to aim as many devices possible and as lower android api level possible.
I also have the option to authenticate on server side based on information received from the device (if there are ways to do it that is not possible by the device itself)
It looks like that you get strange ideas of my question. although it is not related but let me explain to clear things:
In our country each factory has its own marketers that visit markets on regular basis (daily, weekly, monthly,...) based on their product (milk, biscuit, chips, bread, juice, ....), while the factory wants their marketers visit every markets (as they'll loose their shares to their competitives) marketers think differently (as they receive a small percent of their sale), they just visit those markets which will buy for example a thousand of apple juice and skip those who will buy only 10 (which for them the percentage they get doesn't cover the gas money) and when factory calls this markets to see why they were not buying their products anymore, they get to know that their marketers has not visited them for months.
This is the way they want to make sure that their marketers visit every market and not only the good buyers.
Idea is strange, but anyway: You can use (GPS tagged) photo of client, or/and his sign (by stilus on mobile device screen).