Here are some various ways to upload photos using the Graph API. The examples assume you've instantiated the $facebook object and have a valid session for the current user.
1 - Default Application Album of Current User
This example will upload the photo to your default application album of the current user. If the album does not yet exist it will be created.
$args = array('message' => 'Photo Caption');
$args['image'] = '@' . realpath($FILE_PATH);
$data = $facebook->api('/me/photos', 'post', $args);
print_r($data);
2 - Target Album
This example will upload the photo to a specific album.
$args = array('message' => 'Photo Caption');
$args['image'] = '@' . realpath($FILE_PATH);
$data = $facebook->api('/'. $ALBUM_ID . '/photos', 'post', $args);
print_r($data);
3 - Target Album with Access Token
This example will upload a photo to a specific album which requires an access token.
$args = array('message' => 'Photo Caption');
$args['image'] = '@' . realpath($FILE_PATH);
$data = $facebook->api('/'. $ALBUM_ID . '/photos?access_token='. $ACCESS_TOKEN, 'post', $args);
print_r($data);