Margin for inside test of correction tab
We currently create the margin rect as so:
const int imgWidth = sequenceSize.width - 1 - 2 * imageBorderSize - margin;
const int imgHeight = sequenceSize.height - 1 - 2 * imageBorderSize - margin;
const QRectF imgRect(margin, margin, imgWidth, imgHeight);
But the second and third argument are not coordiantes; they are the length of the respective sides. Therefore we should subtract margin twice.