It could be a matter of Quality over Speed..If you have chosen speed, your images, when moving, seem smooth..
When you stop the images to take a picture, the otherwise unnoticed jagged edges become apparent..
I have set my graphics card to Quality, thus sacrificing performance in the Speed range (FPS)
Here's a perhaps relevant article on Anti-aliasing
http://www.pantherproducts.co.uk/Articles/Graphics/anti_aliasing.shtml