Belgian Soldiers.

@annabel , yes, I researched that, which was what made me think they had met and corresponded.

 

@Chimp : the reverse of the photo, with a clearer signature. I wish I'd looked at it sooner!

 

Thank you very much for all the info you have provided.
I've sent an email to the mairie in Anvers (Antwerp, where he was born), in French, asking if they can give me any details about Édouard Vereycken (there can't be two Belgian soldiers with that name, surely!), so I will have to wait and see.