按ID删除帖子每次都失败

I have a newsfeed where people can upload things, and on there I have a delete button. I read a few techniques you could do to delete a row from the database.

I used this one by using input type hidden field etc.

HTML

<form action="logic/delete_post.php" method="GET">
<input type="hidden" name="id" value="?id='.$pica['img_id'].'" />
<input type="submit" name="deleteSubmit" value="Delete" class="delete_post" />
</form>

DELETE_POST.PHP

<?php


if(isset($_GET['deleteSubmit'])) {

    $img_id = substr($_GET['id'],4,6);

    if(isset($_GET['id'])) {

        $result = $mysqli->query("SELECT picas.img_id FROM picas WHERE username='$ses_user'");
        $mysqli->query("DELETE FROM picas WHERE img_id='$img_id'");

        if (mysqli_affected_rows() == 1) {
        echo 'Succes!';
        } else {
            echo 'Damn!';
        }
    }

}


?>

Every comment with help is appreciated!

Remove the questionmark:

<input type="hidden" name="id" value="?id='.$pica['img_id'].'" />
                                      ^

And make this look like this:

<input type="hidden" name="id" value="'.$pica['img_id'].'" />

Then

$img_id = $_GET['id'];

And addslashes() should be used if this is not enabled in PHP.ini for request values.