Output the image URL of an ACF field

images.php

/**
 * This function is intended to help you grab an image uploaded with ACF. 
 * 
 * @param  [string]  $field The ACF field you want to grab content from
 * @param  [string]  $size  The size of the image (defaults to thumbnail)
 * @param  boolean $subfield If the field is in a repeater, you need to use get_sub_field()
 * @uses   get_field()
 * @uses   get_sub_field()
 * @return [string] the URL of the image
 */
function imag_the_acf_image( $field = null, $size, $subfield = false )
{
    global $post;

    $size = isset( $size ) ? $size : 'thumbnail';
    
    if( $subfield == false ){
        $image = get_field( $field, $post->ID );
    }else{
        $image = get_sub_field( $field, $post->ID );
    }

    echo $image['sizes'][$size];
}