Move an image down

Move an image down

I am developing a webpage for images on a carousel. How can I move an
image down in a DIV, or even center it vertically?
Here is my CSS code:
.carousel .item {
height: 900px;
background-color: #777;
}
.carousel-inner > .item > img {
display: block;
margin-left: auto;
margin-right: auto
}
Here is a URL to the webpage in question to show you that the image is too
high: http://www.canninginc.co.nz/canluciddream/screenshots.html
EDIT
Ok, I have edited the code by changing the:
margin-top: 50px;
I am still after the image to be lower in the div. I can increase the top
margin, but this leaves a white background. What would be the best way to
move the image a little bit lower?