If you want to scale only the selected image( that item has to have the selectable flag ), independently of the other images, then you can catch keyboard event with QGraphicsItem::keyPressEvent.
If you want to scale the entire scene at the same time, then you can catch key presses with QGraphicsScene::keyPressEvent.
Please note that you have to subclass QGraphicsItem/QGraphicsScene and override keyPressEvent in order to be able to get key presses.
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