Class-specific Extremal Region Filter algorithm as proposed in :

Neumann L., Matas J.: Real-Time Scene Text Localization and Recognition, CVPR 2012.

High-level C++ interface and implementation of algorithm is in the objdetect module.
C++ example, a test image, and the default classifiers in xml files.

modules/objdetect/include/opencv2/objdetect.hpp

@@ -394,5 +394,6 @@ CV_EXPORTS_W void drawDataMatrixCodes(InputOutputArray image,
 }
 
 #include "opencv2/objdetect/linemod.hpp"
+#include "opencv2/objdetect/erfilter.hpp"
 
 #endif