How do I get poses/expressions right for drawings you might ask? Well, my computer has "Photobooth" on it... I have hundreds of these kind of images. Anyone looking through my computer might think I was really into pictures of myself with strange arm gestures, but no, just drawing reference.
(the last photo is from when I was living in Montreal and may have gone a little "nuts")
I used to also use this program when I had no mirrors in my house (some strange project I guess) for some months to take a photo of the back of my hair when I was cutting it to make sure it was even. So useful.