Base64文字列をJPEGに変換する際の「無効な画像」エラーを修正する方法?

function base64_to_jpeg($base64_string, $output_file) {
    $ifp = fopen( $output_file, "wb" );
    fwrite( $ifp, base64_decode( $base64_string) );
    fclose( $ifp );
    return( $output_file );
}

$image = base64_to_jpeg( $my_base64_string, 'tmp.jpg' );

function base64_to_jpeg($base64_string, $output_file) {
    // open the output file for writing
    $ifp = fopen($output_file, 'wb');

    // split the string on commas
    // $data[0] == "data:image/png;base64"
    // $data[1] == <actual base64 string>
    $data = explode(',', $base64_string);

    // we could add validation here with ensuring count( $data ) > 1
    fwrite($ifp, base64_decode($data[1]));

    // clean up the file resource
    fclose($ifp);

    return $output_file;
}