I imagine that you could alter the source code to put the landmark generation code inside an 'If' logic instruction, so that the landmarks will only update if a certain condition is met (e.g pressing a certain keyboard key to unfreeze it and take an updated snapshot of the landmark positions).
The low-tech alternative would be to just take a screen-capture picture of the screen with the Prt Scrn key so that you have a static image that you can paste intio paint software!
