Caption Outside Box Shadow

the Shadow is on the .aligncenter Class.
You should put the caption outside of the .aligncenter div.

Get a custom CSS plugin and try this:

.wp-caption.aligncenter img {
	-webkit-box-shadow: 3px 3px 3px #7C7C7C;
	box-shadow: 3px 3px 3px #7C7C7C;
}

.wp-caption.aligncenter {
	box-shadow: none;
}

Thanks Stephen

I just placed your code at the end of my CSS file and it worked perfectly without a plugin.