Can't save images inside canvas to png file - php

Question

I need your help.
I try to generate image like this with canvas (two images and text):
This i want
But after I save canvas file via php to png image all images disappear (text is OK)
Where is the problem with images ? I try this two day's but I can do this. I post here my code maybe some one find what I can do.
INDEX index.php
<canvas id="myCanvas" width="500" height="400"></canvas>
<img id="canvasImg"/>
<script>
var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
function loadImages(sources, callback){
var images = {};
var loadedImages = 0;
var numImages = 0;
for(var src in sources){
numImages++;
}
for(var src in sources){
images[src] = new Image();
images[src].onload = function(){
if(++loadedImages >= numImages){
callback(images);
}
};
images[src].src = sources[src];
}
}
var sources = {
arnold : "arnold.jpg",
silvester : "silvester.jpg"
};
loadImages(sources, function(images){
context.drawImage(images.arnold, 20, 20);
context.drawImage(images.silvester, 280, 20);
});
context.font = "15pt Calibri";
context.fillText("Arnold Schwarzenegger", 30, 300);
context.font = "15pt Calibri";
context.fillText("Silvester Stalonne", 310, 300);
var dataURL = canvas.toDataURL();
document.getElementById('canvasImg').src = dataURL;
$.ajax({
type: "POST",
url: "test.php",
data: {
imgBase64: dataURL
}
}).done(function(response) {
console.log('saved: ' + response);
});
</script>
PHP test.php
define('UPLOAD_DIR', 'images/');
$img = $_POST['imgBase64'];
$img = str_replace('data:image/png;base64,', '', $img);
$img = str_replace(' ', '+', $img);
$data = base64_decode($img);
$file = UPLOAD_DIR . uniqid() . '.png';
$success = file_put_contents($file, $data);
//send request to ocr
print $success ? $file : 'Unable to save the file.';