How to make a simple client permission contract for Photography?

You need a 'photo release' form. They're usually not custom-made, like a will, they're standard document. Google 'photo release' and you might see standard versions that you can just download and print.

Most photographers have in their contact that the photos they take belong to THEM. I think this is really unfair, especially if you're doing a wedding or birthday party or whatever and you're paid to be there. But the idea is that the photos are copyrighted so the clients can't copy them themselves, so if they want more copies they have to come to you.

I am occasionally asked to do a wedding or something, and I always tell my customers 'These photos are YOURS. Here's a DVD. I won't hold onto them so YOU should, if you ever might want to make copies.' But I think follow-ups are a big part of a photographer's income.

But if you took photos at an event that you were HIRED to do, and you gave the original digital images to the customer, and didn't use them for anything else, I don't see how you could be sued!

You don't need permission unless you're publishing the photos in some way that makes use of a person's image for advertising or to disparage them, among other state laws. You own the copyright, as an independent contractor. That's the law in the USA and it varies in other countries. If you WANT to give away free licenses to publish, distribute, copy or modify your copyrighted photos, that's up to you. However, under US law, if you do not specifically transfer your copyright to someone else, you and your heirs own it for 70 years after you die.

"Professional camera" and "Instagram" is a contradiction in terms of the highest order. And to be pedantic, there is no such thing as a "professional camera". It's usually something that MWACs and brainless teenage girls talk about, and can thus be dismissed with maximum prejudice.