My daughter and DIL are the same, no photos on internet and before sending an email etc of said kids to anyone else, it’s only right to run it by the parents, we are close relatives but they are not our kids. And our friends are not their friends and maybe they don’t wants strangers (to them) to be in possession of photos of their children. As many posters have said, once out of your hands you have no control of what happens to them.
I keep photos of my grandkids in my purse and show them off, or I’ll show a pic from my mobile but I never send them without checking first.
I don’t think they are being unreasonable, back in our day no one had a physical picture of your kids unless you gave it to them, nowadays young people have to put up with all relatives getting their phones out, taking photos without permission and sharing them without a second thought. The parents wishes should always be respected. They are their children.