During WWI the Rotterdam businessman Anton Kröller would gain a fortune trading in grain, iron ore and coal.
As far as espionage is concerned Kröller is a shady figure. His company Wm. H. Müller & Co. was originally a German company before he married the heiress, Helene Müller. On 5 August 1914 MI1(c) chief Mansfield Cumming, better known as 'C', asked the London manager of Wm. H. Müller & Co. to put agents at six points along the Dutch coast and report on German warship movements. Kröller himself would have regular meetings with the Dutch intelligence service GSIII.
Part of his company was the Batavier Line, a ferry service between Rotterdam and London. In several cases the German naval intelligence service 'N' approached sailors of the Batavier Line to give them information on sightings of British warships.
The photo is on Kröller's "modest" hunting lodge, that he had build in what is nowadays National Park the Hoge Veluwe.