Auto margins don't center image in page

add display:block; and it'll work. Images are inline by default

To clarify, the default width for a block element is auto, which of course fills the entire available width of the containing element.

By setting the margin to auto, the browser assigns half the remaining space to margin-left and the other half to margin-right.

Under some circumstances (such as earlier versions of IE, Gecko, Webkit) and inheritance, elements with position:relative; will prevent margin:0 auto; from working, even if top, right, bottom, and left aren't set.

Setting the element to position:static; (the default) may fix it under these circumstances. Generally, block level elements with a specified width will respect margin:0 auto; using either relative or static positioning.

You can center auto width div using display:table;

div{
margin: 0px auto;
float: none;
display: table;
}