Just noticed something about alt tag on Facebook Profile Image today.
Apparently, they have a very good machine learning algorithm that views what the image is.
Here’s a copy of HTML.
<img class=”profilePic img” alt=”your Profile Photo, Image may contain: 1 person, sky and outdoor” src=”https://scontent-nrt1-1.xx.fbcdn.net/v/t1.0-1/p160x160/13912548_607852372709679_1427594243754593296_n.jpg?oh=5337e25ab3fc878395f3b4e9b1eb36e8&oe=58FC56AE”>
notice the alt tag. it says 1 person, sky and outdoor.