if (isset) to hide an element until it is set

I am attempting to hide an image box until a file has been set within my file upload code. Right now it shows the $preview image box regardless if a file has been set.

What am I doing wrong?

<form action="" method="POST" enctype="multipart/form-data">
    Change your profile picture <br><input type="file" name="file" class="inputbarfile" onchange="readURL(this);">
    <?php
    $preview_file = '<input type="file" name="file" class="inputbarfile" onchange="readURL(this);">';
    $preview =  '<img width="300px" height="200px" id="file" src="#" alt="your image">';
    if (empty($preview_file)) {
        '';
    } else {
        echo $preview;
    } ?>
    <input type="submit" name="create" value="Upload">
</form>