I tried this:
Qt Code: 
  1. [...]
  2. i1 = QtGui.QPixmap('qtg_aircraft.png')
  3.     i2 = QtGui.QPixmap('qtg_locked.png')
  4.  
  5.     alpha = QtGui.QPixmap(QtCore.QSize(24, 24))
  6.     alpha.fill(QtCore.Qt.transparent)
  7.  
  8.     result = QtGui.QPixmap(QtCore.QSize(24, 24))
  9.  
  10.     painter = QtGui.QPainter(result)
  11.  
  12.     brush = QtGui.QBrush(QtCore.Qt.SolidPattern)
  13.     brush.setColor(QtGui.QColor(QtCore.Qt.transparent))
  14.  
  15.     painter.setBrush(brush)
  16.  
  17.     painter.drawPixmap(QtCore.QRect(0, 0, 24, 24),
  18.                        alpha,
  19.                        QtCore.QRect(0, 0, 24, 24))
  20.  
  21.     painter.drawImage(QtCore.QRect(0, 0, 24, 24),
  22.                       i1.toImage(),
  23.                       QtCore.QRect(0, 0, 24, 24))
  24. [...]
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But it do not work... any other idea ?