In the documentation there’s the following:
It turns out that I need to do this with 4 images, is there maybe a way to do this, or a work-around?
That’s an unfortunate limitation of the gallery component we use. One more thing that is pushing us towards a rewrite. Unfortunately we haven’t gotten there yet.
@duncan: thanks for the swift answer.
Is there maybe another way to have thumbnails that show a bigger image in Sparkle apart from the Slideshow? I am trying this with a button right now, but displaying an image on mouse-over doesn’t seem possible.
Anyone with another smart solution? Maybe the code that would achieve this?
I’m new to the program but that might be the ‘on click’ function? I’m using that a lot for multiple images from thumbs.
-Bill
As Woodrow wrote, the “on click” function is the way to go. You can choose the size of the image - make it not too small - and, depending on the size of the original on click it can fill the whole window.
I started to use galleries, but now prefer the “on click” function, because you have much more flexibility with the layout of the page.
Important: In the settings you have to choose at least 2x. And don’t make your original image too small - Sparkle will do that for you.
@Woodrow and @chrisMF: thanks for the extra suggestion. I’ve made quite a few websites in Sparkle so far, but somehow managed to miss this function completely. Will definitely be used in the future! 
Sadly it’s too limited for the site I have to rebuild, so I’m back to dabbing in (very old) Dreamweaver code… 