HM is pro-European so if one wanted to avoid a treason charge wouldn't one want to use say a picture of Boris Johnson or Nigel Farage? One could get away with it then surely? The fact is the troops swear loyalty to the state in the person of the monarch....if the members of our armed forces were citizens of a republic* such instances would be far less frequent and more easily and readily prosecutable...Corbyn is a republican....so any defence council could easily make the case that pretending to assassinate Corbyn was a lawful act...and this is the real issue.....treason is a matter of dates, in this case 400 or so years worth of same...
*You can shut up K I shall go with the herd eschew you should all Ang Sang heroes...