add new field

I would love to see this, too. ??

I did it like this:

first overloaded this class function and added my field extra_field

public function form_fields() {
		return array(
			'image_size',
			'link',
			'link_text',
			'link_classes',
			'text',
			'extra_field',
		);
	}

then used this filter

add_filter( 'simple_image_widget_instance', function( $instance, $new_instance, $old_instance, $id_base ) {

		$instance['show'] = absint( $new_instance['extra_field'] );

		return $instance;
}, 10, 4 );

then added the input field with this action

add_action( 'simple_image_widget_field-extra_field', function( $instance, $that ) {
	?>
	<p>
		<label for="<?php echo esc_attr( $that->get_field_id( 'extra_field' ) ); ?>">Extra field</label>
		<input class="widefat" id="<?php echo esc_attr( $that->get_field_id( 'extra_field' ) ); ?>" name="<?php echo esc_attr( $that->get_field_name( 'extra_field' ) ); ?>" type="number" step="1" min="1" max="" value="<?php echo $instance['extra_field'] ?>">
	</p>
	<?php
}, 10, 2);

Workes good and seemed correct atleast..

Looks good raphaello77! I have a couple of quick suggestions:

1. Instead of overloading the form_fields() method, use the simple_image_widget_fields filter to register your field. Extending the class is good if you want to create an entirely new image-based widget, but not necessary to add a field.
2. Be sure to escape the output in that value attribute!

Hmm I did try that filter but something didnt want to work cant remember exactly what at the moment.. Ill try it again ??

What i am trying to do is to add your great image upload feature (that i really like!!) and combine it with a woocommerce product listing widget and a custom taxonomy selector..

Here it is:
https://github.com/raphaello77/woocommerce-image-upload-and-product-listing-widget/blob/master/image_product_listing_widget.php

I added a whole lot of file extra fields there..

PS: Thanks for a really great plugin Brady!