I was wondering what is the best way to mask images in HTML 5 ?

In fact I would like to display circle thumbnails in a gallery without bothering my client with the preparation of the circular pictures...

So I have, in my opinion, two options : [Canvas masking](http://thinkvitamin.com/code/html5/create-vector-masks-using-the-html5-canvas/) or [old fashioned way](http://www.cssbakery.com/2009/06/background-image.html)

Do you have others ideas ? Best practices ?

Thanks