When capturing a group photo, Rewind captures a burst of images, allowing the user to pick and choose the best facial expressions for each person in the different photos. The selected faces then are immediately composited into a single photograph. This is done directly when the image is taken. Have a look at it here:
The website Android and Me tried Rewind live at Uplinq event last year. Here's a video of it:
Here's a fun little video how users can use Rewind to "choose how they whould like to remember their day".
Any suggestions how you would use it?