We on the Writelike team try to choose images we think are quirky, rich, interesting, and/or have some sense of history or story behind them.
But we provide inspiration images to be helpful, not restrictive. In some lessons we don't provide them at all because we think the effect is too limiting.
We encourage students and teachers to find their own images, but beware students (or yourself) going down rabbit holes trying to find 'just the right' image.
Also note that you can't upload images to Writelike, so if you want to share an image with your class, you'll need to do so via another channel.