thank you

yep,
as the answer was my attempt at humour - trying to tell you i'm not feeling really motivated to spend one thought on this.
You can ask your members to upload a flag - and they might ignore it or upload any flag - fooling you
Or you can code an extra selector to upload a flag - and they might ignore it or select any flag - fooling you
That's why i don't see any advantage here.

Anyway, I simply google the web when i don't know how to get things accomplished - in this case jquery on select change and got https://stackoverflow.com/questions/12750307/jquery-select-change-event-get-selected-option

$('select').on('change', function (e) {
    var optionSelected = $("option:selected", this);
    var valueSelected = this.value;
    ....
});

So, all that's left to do is
- exchanging the too global 'select' by a unique id like '#my_flag_selector'
- adding the same selector to the $extra_field array as 'id' => 'my_flag_selector'
- completing the script with the upload part of the OssnProfile javascript, this time not based on a manually selected file but a filename derived from valueSelected

hmmm.. the battle was an attempt at humour. I was thinking more of an assigned avatar based on a users grade, for instance on a private school site.. I was using the country selector component as a basis for the edit. I was just asking for some community help in figuring out how to grab tha avatar based on a selector.

To be honest,
I have no particular desire for such battles. I would simply ask my members to download a flag from Flagpedia.net. And done. ;)

https://flagpedia.net/index

ps, I know Roman or the Z~man could do this in a matter of minutes, let the battle begin ;)