Source

File: wp-includes/media.php

function wp_get_attachment_image_src( $attachment_id, $size = 'thumbnail', $icon = false ) {
	// Get a thumbnail or intermediate image if there is one.
	$image = image_downsize( $attachment_id, $size );
	if ( ! $image ) {
		$src = false;

		if ( $icon ) {
			$src = wp_mime_type_icon( $attachment_id );

			if ( $src ) {
				/** This filter is documented in wp-includes/post.php */
				$icon_dir = apply_filters( 'icon_dir', ABSPATH . WPINC . '/images/media' );

				$src_file               = $icon_dir . '/' . wp_basename( $src );
				list( $width, $height ) = @getimagesize( $src_file );
			}
		}

		if ( $src && $width && $height ) {
			$image = array( $src, $width, $height, false );
		}
	}
	/**
	 * Filters the attachment image source result.
	 *
	 * @since 4.3.0
	 *
	 * @param array|false  $image         {
	 *     Array of image data, or boolean false if no image is available.
	 *
	 *     @type string $0 Image source URL.
	 *     @type int    $1 Image width in pixels.
	 *     @type int    $2 Image height in pixels.
	 *     @type bool   $3 Whether the image is a resized image.
	 * }
	 * @param int          $attachment_id Image attachment ID.
	 * @param string|int[] $size          Requested size of image. Image size name, or array of width
	 *                                    and height values (in that order).
	 * @param bool         $icon          Whether the image should be treated as an icon.
	 */
	return apply_filters( 'wp_get_attachment_image_src', $image, $attachment_id, $size, $icon );
}