In essence, StillShot takes any video that you have and converts selected frames from it into high quality photos.
The most obvious use of this is when you setup your camera to take a shot, everybody lines up and smiles, you click the button, and suddenly you notice that your camera is set on video mode. With StillShot you have nothing to worry about, just fire up the app, load the video, choose any frame that you want from the video, and save it as a still image.
StillShot is also useful when objects are on the move and it's hard to catch a specific moment.
Of course you can also use StillShot for capturing a special moment from a video and use it as your desktop wallpaper, to send as a photo to a friend, or even to print and frame.
The app can extract frames from any video, without any special requirements. StillShot keeps the original resolution of the video, for example on the iPhone 4s the resolution is 1080p (1920*1080px).
StillShot was created by Macademia Apps, the same guys that created the awesome GroupShot app (if you don't have that app you should definitely get it).