If you don’t mind explaining, what would the parent be?
Not polygon, just any rectangle. The parent element in this case would be the display area where the sprites show up: it's currently a 2:1 aspect ratio. So if I did the naive thing and just gave you width and height, then "10 10" would be 10% of the display width and 10% of the display height, so the image would get stretched to a 2:1 rectangle no matter what size it was initially. That would let you do squash and stretch, but to get an image to be not stretched, you'd have to do the math to convert backwards to the image's actual aspect ratio (like a square image would need to be 10 5). Which seems... inconvenient.
Oh, I mean to have it shown on the VN screen at all times, not in dialogues.
Oh, I see. You can get ink variables in the javascript with story.variablesState["variableName"] but you'd need a way to display it. You could console.log it in continueStory? Or you'd have to find a place to put it in the HTML, maybe add a div or span with an id and get the element with document.getElementById, and then set element.textContent = story.variablesState["variableName"]