It runs a small Yolo 11 nano neural network in your browser with tract. This model predict a human pose with 17 Keypoints based on Ultralytics pretrained model: Nose, Left Eye, Right Eye, Left Ear, Right Ear, Left Shoulder, Right Shoulder, Left Elbow, Right Elbow, Left Wrist, Right Wrist, Left Hip, Right Hip, Left Knee, Right Knee, Left Ankle and Right Ankle.
Since this model fully run on your browser there is no server needed beyond serving the initial asset, this is private by design (You can use whatever photo), no data is collected, if you are in doubt just turn off your network and try the playground (without reloading).