Monocular Camera calibration from image files

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I have a set of images of a checkerboard pattern from a camera whose calibration info I would like to find out. Unfortunately I can only find instructions on how to get the calibration parameters of a camera connected to the device running ROS. Since I can't hook my camera up to my ROS setup I need a way to feed images to the camara calibration tool instead of the camera itself. Is there any way to do this using the ROS package? Alternatively, are there any other tools I could use?

Thanks a lot!