I make about 100 Euro/mo with PhotoSlim (http://photoslimhq.com), a simple windows software to reduce the size of pictures. I built it although there are lot's of apps for image resizing. But they all had either too many options or were too complicated. So i tried to build the simplest possible solution for this problem. I didn't really believe, that anyone would buy it, since there are a lot of free alternatives. So I am quite happy with the outcome.