sample images
Menu->Edit->Rotate/Flip image->Horizontal mirror effect ([Ctrl]+[W]).
push mouse left button on mirror surface line.
drag to object direction, then release mouse button.
wait until finish
Another direction case,
press [Ctrl]+[W].
push mouse left button on mirror surface line.
drag to object direction, then release mouse button.
wait until finish
Menu->Edit->Rotate/Flip image->Vertical mirror effect ([Alt]+[W])
push mouse left button on mirror surface line.
drag to object direction, then release mouse button.
wait until finish