How do I contact Mac mail to find out what the password is that they insist they must have?

I have iPhoto. It used to be great. Now it does a lot of stuff I don’t like, out of nowhere. (I’ll tell you about the other problems later.) All my images are stored on it because that’s where they go when I download them from my shitty camera. Or any camera.
So now suppose I want to send one of these images to someone. First I have to supply Mac Mail with my password. I don’t know what password they want; the password they want isn’t in my little black book of passwords, because when their system was young, they never used to ask me for it. None of my ordinary passwords unlocks it. But there’s no way for me to acquire my password from Them either – these so-called people who know what it should be. What to do? p.s. I hate these people.