problemen met imagepng(imagecreatefromstring())

hoi iedereen,

ik ondervind problemen met het volgende stukje php :
<?php

// path voor de geresizede img.
$resized_path=Settings::$include_path."/uploaded/avatar_realsize/test/avatar/";
//public static function resizeImage($originalImage,$type,$toWidth,$toHeight)

// small 50px x 50px
$small=image::resizeImage($path.$user_id.".png","png",50,50);
imagepng(imagecreatefromstring(file_get_contents($small)), $resized_path.$user_id."_small.png");

// medium 100x100
$medium=image::resizeImage($path.$user_id.".png","png",100,100);
imagepng(imagecreatefromstring(file_get_contents($medium)), $resized_path.$user_id."_medium.png");

// large 250x250
$large=image::resizeImage($path.$user_id.".png","png",250,250);
imagepng(imagecreatefromstring(file_get_contents($large)), $resized_path.$user_id."_large.png");
echo json_encode(array("success"=> true));

?>

de errors die ik krijg zijn de volgende:
<br />
<b>Warning</b>: file_get_contents() expects parameter 1 to be a valid path, resource given in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1436</b><br />
<br />
<b>Warning</b>: imagecreatefromstring(): Empty string or invalid image in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1436</b><br />
<br />
<b>Warning</b>: imagepng() expects parameter 1 to be resource, boolean given in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1436</b><br />
<br />
<b>Warning</b>: file_get_contents() expects parameter 1 to be a valid path, resource given in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1440</b><br />
<br />
<b>Warning</b>: imagecreatefromstring(): Empty string or invalid image in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1440</b><br />
<br />
<b>Warning</b>: imagepng() expects parameter 1 to be resource, boolean given in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1440</b><br />
<br />
<b>Warning</b>: file_get_contents() expects parameter 1 to be a valid path, resource given in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1444</b><br />
<br />
<b>Warning</b>: imagecreatefromstring(): Empty string or invalid image in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1444</b><br />
<br />
<b>Warning</b>: imagepng() expects parameter 1 to be resource, boolean given in <b>D:\Program Files\devel\xampp\htdocs\git\Business-leaders\controller\adminajax_controller.php</b> on line <b>1444</b><br />

lijkt erop dat er iets fout gaat bij het ophalen van het plaatje

[size=xsmall]Toevoeging op 30/05/2013 14:58:31:[/size]

schijnt dat ik gebruik moet maken van de functie imagecopyresampled