You current design works; loading the images once, upon initialization, instead of every time the widget is painted is the right way. I was not suggesting changing that, quite the contrary.

Instead of allocating QImages on the heap, you could allocate QPixmaps directly with the MiaClasse:

Qt Code: 
  1. class MiaClasse /* ... */ {
  2. /* ... */
  3. private:
  4.   QPixmap image1;
  5.   QPixmap image2;
  6. }
  7.  
  8. void MiaClasse::init(){
  9.   image1.load("resources/images/image1.png");
  10.   image2.load("resources/images/image2.png");
  11.   blink = false;
  12. }
  13.  
  14. void MiaClasse::letItBlink(){
  15.   blink = !blink;
  16.   update(); // Call this instead of QWidget::repaint()
  17. }
  18.  
  19. void MiaClasse:: paintEvent(QPaintEvent *) {
  20.   QPainter painter(this);
  21.   painter.drawPixmap(155, 130, image1);
  22.   if(blink)
  23.     painter.drawPixmap(155, 130, image2);
  24. }
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