To flip an image horizontally, you can set its "scaleX" value to "-1"; to flip it vertically, use "scaleY" instead.
That will change the position of the root of the image, though. To prevent that, you could simply call "[image alignPivotToCenter]" on the image.
This can also be animated: just animate "scaleX" or "scaleY" with an SPTween.
EDIT:"alignPivotToCenter" was only added in Sparrow 2.1; for other versions, simply use the following code:
image.pivotX = image.width / 2;
image.pivotY = image.height / 2;