System information (version)

• OpenCV => 4.5.1
• Operating System / Platform => Ubuntu 18.04
• Compiler => gcc 8.4

Detailed description

In order to use cv::legacy::Tracker (https://docs.opencv.org/master/db/dfe/classcv_1_1legacy_1_1Tracker.html), I get a compiler error when including opencv2/tracking/tracking_legacy.hpp

In file included from /home/xxx/opencv-5.4.1/install/include/opencv4/opencv2/tracking/tracking_legacy.hpp:55
...
/home/xxx/opencv-5.4.1/install/include/opencv4/opencv2/tracking/tracking_internals.hpp:18:10: fatal error: opencv2/video/detail/tracking.private.hpp: No such file or directory
 #include "opencv2/video/detail/tracking.private.hpp"
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Steps to reproduce

• Build OpenCV with opencv_contrib, ensure the tracking module is built
• Run the install target and install into a location
• Try to include tracking_legacy.hpp from the installed location (and NOT the opencv source folder)

The following code will trigger the compiler error:

#include <opencv2/tracking.hpp>
#include <opencv2/tracking/tracking_legacy.hpp>

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc