Picture alignment

I have noticed with some themes its hard to align pics... When I edit the picture in advanced editor and use the mragin-bottom: 15px; I can see the picture in the editor jump up as its suppose to but it does not have that effect on the actual page..

Here is my code
<img class="alignleft size-full wp-image-310" style="margin-bottom: 15px;" title="Download My Vcard" src="http://khanhtech.com/wp-content/uploads/2011/11/vcardicon.png" alt="KhahnTech Solutions Vcar" width="40" height="40" />

Can anyone help out to try and push this image up.. Not sure why its not working