The image input has many options. By default if you do not specify any options no problem... Your image will still be uploaded. But, if you want to resize an image, set the quality of the image, or specify thumbnails for the uploaded image you will need to specify those details.
resize If you want to specify a size you will need to include that in the resize object. If you set either height or width to null it will keep the aspect ratio based on the width or height that is set. So, for the example above the width is set to 1000 pixels and since the height is set to null it will resize the image width to 1000 pixels and resize the height based on the current aspect ratio.
quality If you wish to compress the image with a percentage quality you can specify that percentage in the quality key. Typically between 70 and 100% there is little notice of image quality, but the image size may be dramatically lower.
upsize This is only valid if you have set your image to be resized. If you specify your image to resized to 1000 pixels and the image is smaller than 1000 pixels by default it will not upsize that image to the 1000 pixels; however, if you set upsize to true. It will upsize all images to your specified resize values.
thumbnails Thumbnails takes an array of objects. Each object is a new thumbnail that is created. Each object contains 2 values, the name and scale percentage. The name will be attached to your thumbnail image (as an example say the image you uploaded was ABC.jpg a thumbnail with the name of medium would now be created at ABC-medium.jpg). The scale is the percentage amount you want that thumbnail to scale. This value will be a percentage of the resize width and height if specified.