Eu abri uma imagem em umQHBoxLayout. Preciso cortar a imagem aberta e salvar a imagem cortada. Como posso fazer isso no PySide?

import sys
from PySide import QtGui, QtCore

class Example(QtGui.QWidget):

    def __init__(self):
        super(Example, self).__init__()

        self.initUI()

    def initUI(self):      

        hbox = QtGui.QHBoxLayout(self)
        pixmap = QtGui.QPixmap("re.png")

        lbl = QtGui.QLabel(self)
        lbl.setPixmap(pixmap)


        self.rect = QtCore.QRect()


        hbox.addWidget(lbl)
        self.setLayout(hbox)

        self.setGeometry(300, 300, 280, 170)
        self.setWindowTitle('Open Image')
        self.show()   
        # Tried here to implement Qpen      
        #self.painter = QtGui.QPainter(self)    
        #self.painter.setPen(QtGui.QPen(QtCore.Qt.black, 1, QtCore.Qt.SolidLine));
        #self.painter.drawRect(self.rect);
def main():

    app = QtGui.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()