default.crop

If default.crop is set to rule-of-thirds, then the default vertical positioning of crops is based on the "rule-of-thirds". This means that instead of being centered on the true vertical center of the original image, they are centered on a line drawn one-third of the distance from the top of the image. This is a better choice for many kinds of image. It is more likely, for example, to include people's faces.

For example:

default.crop=rule-of-thirds