When pulling a set of images using an Images widget, by default they will be generated at the largest possible values that fit within your specified width and height settings without cropping.

With crop=true, all images will be cropped to that exact width/height (provided they are large enough). Images that are too small to be cropped to those dimensions will be cropped to the nearest fit.

<widget type="images">
        <arg id="tag">Featured</arg>
        <arg id="width">800</arg>
        <arg id="height">600</arg>
        <arg id="crop">true</arg>
</widget>