This is an example of the same Hero Image, but it is uncropped. The photo is 1600X1065. When that photo is used in the Hero Image, The Hero Image vertically centers the image and then takes the middle 500 pixels to display.
In the image below, the full image is shown, along with a box showing you what is actually displayed in your Hero Image if you do not crop it. For some images, this will work just fine. Other times you will want to crop it to get a better looking image.