http://study.marearts.com/2014/03/opencv-study-write-text-on-image.html
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//cvPutText, IplImage case.

CvFont * font = new CvFont;
cvInitFont(font, CV_FONT_VECTOR0, 0.5f, 1.0f, 0, 1, 8); //rate of width and height is 1:2
char szText[8];
sprintf(szText, "TextOut");  //make string
cvPutText(Image, szText, CenterPoint, font, CV_RGB(255, 255, 255)); //draw text on the IplImage* (Image)



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//putText, Mat case.

char TestStr[100]; 
sprintf(TestStr,"total time : %lf sec", 0.001 );
putText(OutImg, TestStr, Point(100,250), CV_FONT_NORMAL, 1, Scalar(255,255,255),1,1); //OutImg is Mat class;