Picture uploading proble - php

Question

I don't have an idea why it doesn't upload pictures(But the same peace of code does). Please help me.
HTML:
$max_filesize = 524288;
$upload_path = './img/';
$id=$_POST["id"];
for ($i=1; $i<=3; $i++)
{
(string)$inside="inside".$i;
echo $inside;
$filename = $_FILES[$inside]['name'];
echo $filename;
$ext = substr($filename, strpos($filename,'.'), strlen($filename)-1);
echo $ext;
if (isset($_POST[$inside])){
if(filesize($_FILES[$inside]['tmp_name']) > $max_filesize)
die('File is too big.');
if(!is_writable($upload_path))
die('Cannot access folder - 777.');
if(move_uploaded_file($_FILES[$inside]['tmp_name'],$upload_path . $id . "inside" . $i . $ext))
{
echo 'Uploaded successfuly ';
echo '<br><br>';
echo '<img src="' . $upload_path . $filename . '" width="300" >';
} else {
echo 'Something went wrong, try again.';
}
}
}
Before that:
<form method="post" enctype="multipart/form-data" action=""/>
Що в коробці(Фото): <p>
<input type="file" name="inside1"
accept=".jpg, .jpeg, .png"> <p>
<input type="file" name="inside2"
accept=".jpg, .jpeg, .png"> <p>
<input type="file" name="inside3"
accept=".jpg, .jpeg, .png"> <p>
</form>
It says 'Something went wrong, try again.'.

Answer 1

Strange form - <form></form>
<form action="<?php echo'admin/photo_upload.php'; ?>" enctype="multipart/form-data" method="POST">
<input type="hidden" name="MAX_FILE_SIZE" value="<?php echo $max_file_size; ?>" />
<p><input name="file_upload[]" type="file" id="file_upload[]" value=""></p>
<p><input name="file_upload[]" type="file" id="file_upload[]" value=""></p>
<p>Caption: <input type="text" name="caption" value="" /></p>
<input type="submit" name="submit" value="Upload" />