How can I add or import a picture to a QWidget?

A generic QWidget does not have setPixmap(). If this approach does not work for you, you can look at making your own custom widget that derives from QWidget and override the paintEvent method to display the image.

import os,sys
from PyQt4 import QtGui

app = QtGui.QApplication(sys.argv)
window = QtGui.QMainWindow()
window.setGeometry(0, 0, 400, 200)

pic = QtGui.QLabel(window)
pic.setGeometry(10, 10, 400, 100)
#use full ABSOLUTE path to the image, not relative
pic.setPixmap(QtGui.QPixmap(os.getcwd() + "/logo.png"))

window.show()
sys.exit(app.exec_())