PHP MYSQL - 图像上传错误

I'm totally new using databases, so maybe my problem is something obvious. My variables are in danish, I hope you'll understand anyway. I have already searched in the forum, but because this is new to me, I find it very hard to understand.

A user should create a profile with a profile picture, but an error happens when I try to save it. My own defined error pops up because $billednavn == false.

The code:

<?php  

// 1. Gem modtagne formulardata i variabler:  
$navn = $_POST['navn'];  
$alder = $_POST['alder'];  
$postnr = $_POST['postnr'];  
$mail = $_POST['mail'];  
$billede = $_FILES['profilbillede'];  
$password = $_POST['password'];  



// 2. Forbind til databasen:  
$databaselink = mysqli_connect("localhost","mmddk3e12m8b18", "****", "mmddk3e12m8b18") or die     ("Fejl: Kan ikke etablere forbindelse til database");



$billednavn = billedupload($billede);  
// besked til brugeren om at der er sket en fejl    
if($billednavn == false){  
die("Der skete en fejl under upload af billedet");
}



// 3. Udform insert SQL streng med de modtagne data, og udfør SQL strengen på databasen vha     mysqli_query:  
$query = "INSERT INTO brugere (navn, alder, postnr, mail, password, profilbillede) VALUES ('$navn', '$alder', '$postnr', '$mail', '$password', '$billednavn')";  
$result = mysqli_query($databaselink, $query) or die( "Forespørgslen kunne ikke udføres: " .         mysqli_error($databaselink));  

// 4. luk databasen:  
mysqli_close($databaselink);  

function billedupload($fil){  
if($fil['type']=='image/jpeg' or $fil['type']=='image/png'){  
$tmp_navn = $fil['tmp_name'];  
$filnavn = $fil['name'];  
$target = 'images/' . time() . $filnavn;  
move_uploaded_file($tmp_navn,$target);  
return $target;  
}  
else{  
return false;  
}  
}  

?>

If it returns false, then - by your definition, either the file type isn't image/jpeg or it isn't image/png, or the type isn't set, or the entire $_FILES isn't set.

In your HTML form make sure you have <form enctype="multipart/form-data" method="POST"> and try var_dump($_FILES); in your PHP file to validate your POST data.

EDIT: In the condition where tmp_name is empty there are two possible situations i can think of:

You forgot to set <form enctype="multipart/form-data"> (more likely, please validate that)
In your php.ini make sure file_uploads are set to On

The first option is more probable, Of course.