我注意到Google Images正在使用画布渲染图像. < IMG>用作不支持画布的浏览器的后备.

<a class="rg_l" style="..." href="...">
  <canvas
    id="cvs_NcG8skPEDu7FWM:b"
    style="display:block"
    width="83"
    height="113">
  </canvas>
  <img 
    class="rg_i"
    id="NcG8skPEDu7FWM:b"
    src="http://t0.gstatic.com/images?q=tbn:ANd9GcQCB5NEbEUQhtmFI098HLSkfmoHTBtUfERUNkNKrhgFbtFBxZXY9ejXn_pUGg"
    height="113"
    width="83"
    style="width:83px;height:113px"
    onload="google.isr.fillCanvas(this);google.stb.csi.onTbn(0,this)"
    src="http://t0.gstatic.com/images?q=tbn:ANd9GcQCB5NEbEUQhtmFI098HLSkfmoHTBtUfERUNkNKrhgFbtFBxZXY9ejXn_pUGg">
</a>

使用< canvas>的重点是什么？而不是< img>？