SecurePose is an open source software that provides reliable de-identification and automated kinematics extraction simultaneously from videos taken in a clinical environment with smartphones/tablets. It extracts full body kinematics via pose estimation using OpenPose, identifies patients by tracking individuals, and then blurs faces accurately in the videos. Using 116 gait videos of children with cerebral palsy, it evaluates the de-identification accuracy and the reliability of the intermediate step of kinematics extraction, showing that it outperforms six existing methods in automatic face detection and achieves similar accuracy as manual blurring much faster (91.08% faster). Ten experts validated the usability of SecurePose through the system usability scale scores. These results demonstrate that SecurePose is a practical and effective tool that enables accurate kinematics extraction in clinical settings while protecting patient privacy.