Advanced Custom Fields - Update Image / File with Gravity Forms

functions.php

// Front Raw
$gravity_form_id = 6; // gravity form id, or replace {$gravity_form_id} below with this number
add_filter("gform_after_submission_{$gravity_form_id}", 'eve_set_front_raw_image_field', 10, 2);
function eve_set_front_raw_image_field($entry, $form){
	$gf_images_field_id = 50; // the upload field id
	$acf_field_id = 'field_54ca50b09afe2'; // the acf front raw field id

	// get post
	if (isset($entry['post_id'])) {
		$post = get_post($entry['post_id']);
		if (is_null($post)) return;
	}
	else {
		return;
	}
	// Clean up images upload and create array for front raw field
	if (isset($entry[$gf_images_field_id])) {
		$images = stripslashes($entry[$gf_images_field_id]);
		$images = json_decode($images, true);
		if (!empty($images) && is_array($images)) {
			foreach($images as $key => $value) {
				// NOTE: this is the other function you need: https://gist.github.com/joshuadavidnelson/164a0a0744f0693d5746
				if (function_exists('jdn_create_image_id')) $image_id = jdn_create_image_id($value, $post->ID);
				if ($image_id) {
					$gallery = $image_id;
				}
			}
		}
	}

	// Update front raw field with array
	if (!empty($gallery)) {
		update_field($acf_field_id, $gallery, $post->ID);
		// Updating post
		wp_update_post($post);
	}
}

required.php

/**
 * Create the image attachment and return the new media upload id.
 *
 * @since 1.0.0
 * @see http://codex.wordpress.org/Function_Reference/wp_insert_attachment#Example
 */
function jdn_create_image_id( $image_url, $parent_post_id = null ) {
	
	if( !isset( $image_url ) )
		return false;

	// Cache info on the wp uploads dir
	$wp_upload_dir = wp_upload_dir();
	// get the file path
	$path = parse_url( $image_url, PHP_URL_PATH );

	// File base name
	$file_base_name = basename( $image_url );

	// Full path
	if( site_url() != home_url() ) {
		$home_path = dirname( dirname( dirname( dirname( dirname( __FILE__ ) ) ) ) );
	} else {
		$home_path = dirname( dirname( dirname( dirname( __FILE__ ) ) ) );
	}

	$home_path = untrailingslashit( $home_path );
	$uploaded_file_path = $home_path . $path;
	// Check the type of file. We'll use this as the 'post_mime_type'.
	$filetype = wp_check_filetype( $file_base_name, null );

	// error check
	if( !empty( $filetype ) && is_array( $filetype ) ) {
		// Create attachment title
		$post_title = preg_replace( '/\.[^.]+$/', '', $file_base_name );
	
		// Prepare an array of post data for the attachment.
		$attachment = array(
			'guid'           => $wp_upload_dir['url'] . '/' . basename( $uploaded_file_path ), 
			'post_mime_type' => $filetype['type'],
			'post_title'     => esc_attr( $post_title ),
			'post_content'   => '',
			'post_status'    => 'inherit'
		);
	
		// Set the post parent id if there is one
		if( !is_null( $parent_post_id ) )
			$attachment['post_parent'] = $parent_post_id;
		// Insert the attachment.
		$attach_id = wp_insert_attachment( $attachment, $uploaded_file_path );
		//Error check
		if( !is_wp_error( $attach_id ) ) {
			//Generate wp attachment meta data
			if( file_exists( ABSPATH . 'wp-admin/includes/image.php') && file_exists( ABSPATH . 'wp-admin/includes/media.php') ) {
				require_once( ABSPATH . 'wp-admin/includes/image.php' );
				require_once( ABSPATH . 'wp-admin/includes/media.php' );
				$attach_data = wp_generate_attachment_metadata( $attach_id, $uploaded_file_path );
				wp_update_attachment_metadata( $attach_id, $attach_data );
			} // end if file exists check
		} // end if error check

		return $attach_id; 

	} else {
		return false;
	} // end if $$filetype
} // end function get_image_id