How to make rectangular image appear circular with CSS

I presume that your problem with background-image is that it would be inefficient with a source for each image inside a stylesheet. My suggestion is to set the source inline:

<div style="background-image: url(image.gif)"></div>

div {
    background-repeat: no-repeat;
    background-position: 50%;
    border-radius: 50%;
    width: 100px;
    height: 100px;
}

Fiddle