Move the Vertical perspective slider. If the photo object appears to be leaning backwards, move the slider to the left. Tall buildings in photos usually appear to be leaning back when the picture is taken from the ground.

Move the Horizontal perspective slider. If the photo was taken with the camera to the right of the object, move the slider to the left.

Enable the Crop check box, and then enable the Crop and resample to original size check box.