Centering an image in CSS

Hi guys,
I am in a bit of a pickle here. I have been trying to center an image in a div, but cannot seem to do it.
I have searched and found this thread, but it hasnt helped.

Basically I have:

#picture_nest
{
padding: 0px;
display: block;
float: left;
width: 143px;
margin-left: 0px;
}
.picture {
text-align: center;
}

and I have it as so:

<div id=“picture_nest”><span class=“picture”><img src=“blah.jpg”></span></div>

But obvioulsy “text-align: center;” is not working.

Any ideas ?

Cheers,
D