Google image search shows thumbnails of images that fit in their search results layout. If the aspect ratio doesn't allow it to fit into the layout, Google crops the image. Google crops the thumbnails show in the search results that are either too tall or to wide.
It looks like the tallest images you can use without cropping have an aspect ratio of about 7:9. To prevent Google from cropping your images in the search results, increase the image width.
For some searches, almost all the images are a taller aspect ratio than what fits in the search results layout. If you search for "standing woman", almost all the results show women with parts of their heads or feet cropped off. There are a couple that are not cropped though. Note that the image from 3D Warehouse on the right of the screenshot below is not cropped. That image has plenty of white space on the right and left making the aspect ratio of the image wider than tall.