Could you show me examples of "addText" and "displayOverlay"

edit

you have to (re)build opencv with QT support to use those those functions.

if all you want is some text, use putText

oh, btw, the order of calls matters, too.

displayOverlay("horizontal", text); // first draw,
imshow("horizontal", H);            // then show it
waitKey(someMillis);                // imshow won't work without