Visual Composer creating own shortcodes with vc_map() to return simple Image

Visual Composer adds the image ID to the generated shortcode. This gives you more flexibility with image sizes. You can use it like this:

$imageSrc = wp_get_attachment_image_src($image_url, 'thumbnail');
if( $imageSrc ) {
    echo '<img src="' . $imageSrc[0] . '" />';
}

The thumbnail param could be replaced by medium or another valid image size. The if clause is there to verify that the image is really there (not deleted).

Advice: Rename the param_name to image_id so you won’t get confused when using the code later.

Source: https://developer.wordpress.org/reference/functions/wp_get_attachment_image_src/