Sadly in the Netherlands and Belgium, I have been stopped more times than I can remember in the last few years. On the Dutch side it has been particularly bad between Terneuzen and Walsoorden, when I have asked it has always been because of 'Drugs' and my interest in ships and the river. More recently it has felt it was because I am in a British car, as they never seem to take an interest in the locals?
In Antwerp a few years ago at the Boudewijnsluis I was stopped by a port official not for taking photos but for concerns I was fishing, something that is now banned along the Belgium part of the river after it was implied Eastern Europeans had cleared the river of Fish stocks.
In the 90's I was occasionally stopped in Antwerp and my passport checked by the Police, but never told
I couldn’t take photos. In fact I am old enough to remember the Port of Antwerp once issued written permission to take photos, a letter I kept with me & I can remember using it at least once when challenged by a private guard. Ghent was another Belgium port that issued photo permits.
Last year I was challenged, whilst standing outside the fence of a container terminal in Antwerp, near the Berendrechtsluis, I had no idea what he was saying or what his problem was, so politely smiled and moved on.
I think we have to assume recruits joining modern Police, Customs, Security agencies etc, are now being trained to root out drugs and terrorists like never before and I don't suppose anyone has educated them on Ship Enthusiasts, that were once welcomed in Ports, but now have to reside on the banks of rivers etc. Sadly being stopped by officials seems to be one of things we have to occasionally accept in the modern world as an Enthusiast of most modes transport.
I believe hand held scanners are banned in Belgium, I don’t know if this is still the case?