This is not really an IMDB API. There doesn't seem to be a way to use IMDB API for free anyway. However this API does returns movies, is free and has database big enough for most cases.
Getting movie or tv show information from PHP using free API:
$imdbID = 'tt2866360';
$data = json_decode(file_get_contents('http://api.rest7.com/v1/movie_info.php?imdb=' . $imdbID));
if (@$data->success !== 1)