By default, the Layout setting of an Image is set to cover, which means the Image will be resized to completely cover the element and parts may be cropped out, depending on the difference between the aspect ratios of the actual image and the Image Element box.
There are three other possible Layout settings that you can apply to show your entire image.
Contain will resize your image so that it is the largest it can be while remaining within the element box.
Fill will stretch your image so that it fills the entire element box.
Scale-down will resize your image whilst maintaining its original proportions so that the whole image is visible. If the element box is larger than the uploaded image, the image will be displayed in the center of the box, at its original size.