Can't build OSIRIS makefile

[gxporpilla]

Having some trouble building the makefile. According to my inquiries, the cvMean is part of the OpenCV old C API and is deprecated. Should I install an older version of OpenCV? Already tried OpenCV 4 and downgraded to 3 but still the same error.
OsiProcessings.cpp:299:28: error: ‘cvMean’ was not declared in this scope
double iris_mean = cvMean(pSrc,safe_area) ;
^~~~~~

Raspberry Pi 4 Buster
Python 3.7.3
OpenCV 3.4.19-dev