ImageAspectRatio

ImageAspectRatio[image] gives the ratio of height to width for image.

Examples

Get aspect ratio:

img = ExampleData[{"TestImage", "Lena"}];
ImageAspectRatio[img]
(* 1. *)

Compare with dimensions:

ImageDimensions[img]
(* {512, 512} *)

Please visit the official Wolfram Language Reference for more details.