UIImageView does not respond to touch gestures. You'll need to subclass it and then attach the gesture listener to each view. From here:
A UIImageView is derived from a UIView which is derived from
UIResponder so it's ready to handle touch events. You'll want to
provide the touchesBegan, touchesMoved, and touchesEnded methods and
they'll get called if the user taps the image. If all you want is a
tap event, it's easier to just use a custom button with the image set
as the button image. But if you want finer-grain control over taps,
moves, etc. this is the way to go.
You'll also want to look at a few more things:
Override canBecomeFirstResponder and return YES to indicate that the
view can become the focus of touch events (the default is NO).
Set the userInteractionEnabled property to YES. The default for
UIViews is YES, but for UIImageViews is NO so you have to explicitly
turn it on.
If you want to respond to multi-touch events (i.e. pinch, zoom, etc)
you'll want to set multipleTouchEnabled to YES.