How to save img to user’s local computer using HTML2canvas

NOTE: this answer is from 2015 and the library has been updated.
Check the answers below for alternate implementations.

Try this (Note that it makes use of the download attribute. See the caniuse support table for browsers that support the download attribute)

<script>

  $('#save_image_locally').click(function(){
    html2canvas($('#imagesave'), 
    {
      onrendered: function (canvas) {
        var a = document.createElement('a');
        // toDataURL defaults to png, so we need to request a jpeg, then convert for file download.
        a.href = canvas.toDataURL("image/jpeg").replace("image/jpeg", "image/octet-stream");
        a.download = 'somefilename.jpg';
        a.click();
      }
    });
  });

</script>