About DYC ImageURL field

I’ve been searching the sketchup documentation for some time about the imageIMG field in the development of dynamic components and I haven’t found anything about the aspect ratio of this image. My problem is to define an image with correct proportion to avoid distortion since it is not possible to define it manually because the width and height fields refer to the component attributes window.

Doing some tests here I found the ratio of 128:83 and I would like to know if anyone else has reached this result or a different one.