Taking a Screenshot of Webpage

I would like to take screenshot of webpages and let the users download as PNG files. my code is working fine, but it is not capturing some image elements.

What am I doing wrong.

Here is the code

<!-- https://github.com/niklasvh/html2canvas -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/1.3.4/html2canvas.min.js"></script>
<script>
function capture () {
  html2canvas(document.body).then((canvas) => {
    let a = document.createElement("a");
    a.download = "ss.png";
    a.href = canvas.toDataURL("image/png");
    a.click();
  });
}
</script>
<input type="button" value="Capture" onclick="capture()"/>

And the results from this code is this capture

But my website looks kind of like this, clearly you can see what is missing