canvas.toDataURL() generate wrong DataURL

canvas.toDataURL() generate wrong DataURL

What's the problem with toDataURL() function in my code!?
My problem is, the p0 canvas will remain empty!
After uploading my image in dataurl.net, i found out, it DataUrl code and
my DataUrl code that was saved in LocalStorage are different!! and that's
why it can't show anything!
<canvas id="p0" width="512" height="176" style="margin-left: 200px;
margin-top: 216px; position: absolute"></canvas>
<script>
function init() {
var p0 = document.getElementById("p0");
var P0 = p0.getContext('2d');
var img = new Image;
img.onload = function () {
P0.drawImage(img, 0, 0);
};
if (localStorage.getItem("version") == Version) {
img.src = localStorage.getItem("p0");
} else {
localStorage.setItem("version", Version);
img.src = "Index/2/logo.png";
localStorage.setItem("p0", p0.toDataURL("image/png"));
}
}
init();
</script>