Just check for the current Facebook user id $user and if it returned null then you need to reauthorize the user (or use the custom $_SESSION user id value - not recommended)
require 'facebook/src/facebook.php';
// Create our Application instance (replace this with your appId and secret).
$facebook = new Facebook(array(
'appId' => 'APP_ID',
'secret' => 'APP_SECRET',
));
$user = $facebook->getUser();
$photo_details = array('message' => 'my place');
$file='photos/my.jpg'; //Example image file
$photo_details['image'] = '@' . realpath($file);
if ($user) {
try {
// We have a valid FB session, so we can use 'me'
$upload_photo = $facebook->api('/me/photos', 'post', $photo_details);
} catch (FacebookApiException $e) {
error_log($e);
}
}
// login or logout url will be needed depending on current user state.
if ($user) {
$logoutUrl = $facebook->getLogoutUrl();
} else {
// redirect to Facebook login to get a fresh user access_token
$loginUrl = $facebook->getLoginUrl();
header('Location: ' . $loginUrl);
}
I've written a tutorial on how to upload a picture to the user's wall.