Download the no-install version of labelImg from the link: https://github.com/tzutalin/labelImg/releases;
Unzip the file to get the exe file of labelImg, double-click to run labelImg without installation.
Modify the file predefined_classes.txt, only keep the line 'person';
Click Open Dir to open the image directory;
Click Change Save Dir to open the annotation directory;
Check the Use default label option and fill in person to speed up the labeling;
Click on Create RectBox on the left (shortcut key W), and then select the object;
Click Save to save the label (shortcut key Ctrl+S);
Click Next Image to label the next image (shortcut key D).