I think that your answer on the Dutch painting is correct. And yes, it's calculus, and next to it maybe a drawing of sails! Amazing. This is great, because if you are "infected" (or even curious),you have big chances to "pass" it to your students. Imagine: even the English teacher thinks Maths can be fun,this is a strong argument! More than if a Math teacher says it!The site looks really interesting, I have to look it thoroughly. Thanks!
This was also my idea. A unit circle to explain the sin, cos and tan functions!How nice that you are coming to enjoy mathematics!!!