In addition to its common properties, the image element has several properties of its own.
|The URL of an image (a jpg, png, or svg) you want to display. If it was uploaded using the template editor, it may also be its internal GUID.
|This property specifies how the image should be resized to fit the element. It can be set to cover, contain, or fill.
|Experimental feature. If smart cropping is enabled and fit is set to cover, an edge detection algorithm scans the image to find the best cropping.
Check out the template editor's documentation on the image element as well.