Working with sprite nodes in swift

sprite.swift

// create image sprite
let img = SKSpriteNode(imageNamed:"ImageName");

// scale the image            
img.xScale = 0.5;
img.yScale = 0.5;

// set the image position
 
img.position = CGPoint(x: 100, y: 100);
// centering the image
img.position = CGpoint(x: CGRectGetMidX(self.frame), y: CGRectGetMidY(self.frame))
// determine the position from touch event
// must have access to touch (ie: func touchesBegan(touches: NSSet....)
img.position = touch.locationInNode(self); 

// add sprite to view
self.addChild(sprite)