OpenCVopencv/opencv
OpenCV has C++, C, Python, Java and MATLAB interfaces and supports Windows, Linux, Android and Mac OS.

ukoethe/vigra
VIGRA is a genertic cross-platform C++ computer vision and machine learning library for volumes of arbitrary dimensionality with Python bindings.
OpenCV has C++, C, Python, Java and MATLAB interfaces and supports Windows, Linux, Android and Mac OS.
A real-time multi-person keypoint detection library for body, face, hands, and foot estimation
DLib has C++ and Python interfaces for face detection and training general object detectors.
A machine learning API and server written in C++11. It makes state of the art machine learning easy to work with and integrate into existing applications.
A C++ edge video AI engine for RTSP ingestion, CV/VLM inference, visual pipeline orchestration, alarms, and event delivery on Sophon and Rockchip NPUs.
The Gesture Recognition Toolkit (GRT) is a cross-platform, open-source, C++ machine learning library designed for real-time gesture recognition.
Eblearn is an object-oriented C++ library that implements various machine learning models
A deep learning framework developed with cleanliness, readability, and speed in mind.