<html>
<script>
function watermark(str){
var img = document.getElementById("img");
var canvas=document.getElementById("cvs");
var ctx=canvas.getContext("2d");
ctx.drawImage(img,0,0);
ctx.font="20px microsoft yahei";
ctx.fillStyle = "rgba(255,255,255,0.5)";
ctx.fillText(str,100,100);
}
script>
<canvas id="cvs" width="1000" height="500" >
Your browser does not support the HTML5 canvas tag.
canvas>
<image id="img" src="test.png" > image>
<button onclick="watermark('Hello world')">add watermarkbutton>
html>
