Save screenshot using html2canvas to web folder - php

Question

I have a website, where user can take screenshot of that website and that screenshot should save automaticly to folder "posters" inside my "www" folder.
But when I try to make an screenshot, it is saved directly to "www" folder and not to the "posters" folder. I tried to change atributes of the "posters" folder to 777 but It did not helped. And also, that "posters" folder gives this error: Forbidden You don't have permission to access /posters/ on this server. when I try to visit it via browser. I dont know what is wrong.
Here is my save.php code:
<?php
//Get the base-64 string from data
$filteredData = substr($_POST['img_val'], strpos($_POST['img_val'], ",") + 1);
//Decode the string
$unencodedData = base64_decode($filteredData);
//Save the image
file_put_contents('img_' . date("U") . '.png', $unencodedData);
move_uploaded_file('img.png', './posters/$newname');
?>
<h2>Save the image and show to user</h2>
<table>
<tr>
<td>
<a href="img.png" target="blank">
Click Here to See The Image Saved to Server</a>
</td>
<td align="right">
<a href="index.php">
Click Here to Go Back</a>
</td>
</tr>
<tr>
<td colspan="2">
<br />
<br />
<span>
Here is Client-sided image:
</span>
<br />
<?php
//Show the image
echo '<img src="' . $_POST['img_val'] . '" />';
?>
</td>
</tr>
</table>
<style type="text/css">
body, a, span {
font-family: Tahoma; font-size: 10pt; font-weight: bold;
}
</style>
Is it possible to make something like this? file_put_contents(.PathToFolder/'img_' . date("U") . '.png', $unencodedData);