What we'll do here is use css border property for outer image border and we'll fake the inner border using combination of background and padding properties.

First we add a border property to the image and set the values

img{
 border:2px solid #72a143;
}

If we set the padding to 1px and add a yellow background,

img{
 border:2px solid #72a143;
 padding:1px;
 background:#ffeda5;
}

the image will receive another "border" inside the real one.
That's it! :)

补充一下，其实这个很容易变通成为图片加上阴影，只需要在用一个阴影图片就行了，右和下加padding