I have a soft spot for old postcards and often try to find them to enhance my stamp collection. That way, I've already got quite a few Wilhelmina postcards. I do, though, try and limit myself to postcards that have a function within the collection, so not just any portrait postcard of Wilhelmina would be suitable. But have a look at this beauty.
It's a postcard with a photograph of court photographer Deutmann in The Hague. And the reason I'm so happy to have got it, is that this is the portrait that was used for the 1923 Jubilee stamps of the Dutch overseas territories. Here's a closer look at the portrait.
That same portrait was then subsequently used for various definitives, like this Curaçao set.
When funds do not permit the purchase of die proofs and other design material, this is a great way of being able to tell a bit more about the stamps you collect!