It would all depend on how the system is set up. It could be set to delete the image, then destroy it by overwriting it's data with nonsense data, making it impossible to recover. That's real easy to build into the machines.

It would make sense that the image was deleted every time somebody was given the clear signal, or the last five minutes or whatever, much like many police cars cameras, while always on, only store the last 90 seconds to when the flashing lights come on or they activate the camera, saving only the previous 90 seconds and everything going forward from that point.

So the technology is available to do those things but it's just a question of is it being implemented or not.

I would believe not, if you want to prosecute somebody, you will need to match the image of them going through the checkpoint to the scanned image. There's gonna be some xplainign to do the first time a case goes to court and they pull up all the images they say they don't have.