There is one other safety issue here - when I am watching a trespasser I have taken my eye of the track ahead and many drivers will lose concentration momentarily, you also have to call the signaller with the GSMR using the priority or emergency call all depending on the situation and this in turn will cause a driver to lose concentration on the job at hand.
I reported a trespasser approaching Warrington a few months back and also another at Frodsham, both occasions I hade to shut the power off and brake the train and at the same time look for a reference point for an exact location, also I am slowing for the station and watching signals, the signaller taking the call from the driver will also go through the same distraction and may inadvertently hold a signal at red that another driver may pass. This sets up a risk that could under some circumstances cause an incident where the driver will need to be spoken to, taken off track and possibly specially monitored all because a spotter wanted a better picture. Sorry but this sort of thing needs to stop and those trespassing should be named, shamed and prosecuted.
While you good guys are out and about maybe if you see trespasser take a snap shot of them and post it on here if that is legal