Simple function to convert a base64 image string to its original format. Should only be used with trusted data!

base64_to_image.php

<?php
function base64_to_image( string $base64_string, string $output_filename = '', string $output_dir = '_base64-out' ): string|false
{
  $data = explode( ',', $base64_string );
  $mime = substr( explode( ';', $data[0] )[0], 5 );
  $ext  = explode( '/', $mime )[1];

  if ( ! str_starts_with( $mime, 'image' ) )
    throw new InvalidArgumentException( 'Invalid image mime type data.' );

  $output_file = ( empty( $output_filename ) )
    ? $output_dir . '/base64-' . time()
    : $output_dir . '/' . $output_filename;
  $output_file .= '.' . $ext;

  if ( false !== file_put_contents( $output_file, base64_decode( $data[1] ) ) )
    return $output_file;
  else return false;
}