How can I part identification in real time using kinect?

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If by parts you mean human body parts, you can use OpenNI skeleton tracker to achieve your goal. The official ROS port is available from here. Prior to using this package, you need to install NITE library based on the instruction provided in openni_tracker's readme file. You can check this tutorial for more information. Please note that the binary installation for this package is available only up to ROS Hydro which has recently been end of lifed. You may be able to compile openni_tracker from source as discussed in this thread if you are using Indigo.

There seems to be a newer version of this package based on OpenNI2 called openni2_tracker. Unfortunately there is no ROS wiki page about this package and no documentation.