1. An image generating apparatus which generates a second image that is an image converted from a first image captured by an imaging apparatus placed to be oriented downward at an angle of depression with respect to a horizontal direction, said image generating apparatus comprising: a specifying unit configured to specify a straight line included in the first image and passing through an intersection between an imaging plane and a vertical vector having a start point at the imaging apparatus; and an image extension processing unit configured to generate the second image by sampling pixels of the first image along the specified straight line, wherein said specifying unit is configured to specify the pixels included in the specified straight line, the generated second image includes the sampled and specified pixels as pixels included in a straight line in a top-bottom direction of the second image, the specified straight line is a straight line passing through a first intersection that is the intersection and a second intersection, and the second intersection is an intersection between the imaging plane and a third vector generated by rotating a second vector around a first vector as a rotational axis, the first vector being the vertical vector, and the second vector having a start point at the imaging apparatus.