onload="fixImage(this, 200, 200)"

function fixImage(img, w, h) {
    var newImg = new Image(); //获得图片的原始尺寸
    newImg.src = img.src;
    var lh;  //用于保存img.height，IE下隐藏的图片读取不到，需currentStyle解决
    if (newImg.width / newImg.height >= w / h) {
        if (newImg.width > w) {
            img.width = w;
            img.height = w * newImg.height / newImg.width;
            lh = window.ActiveXObject ? parseInt(img.currentStyle['height']) : img.height;
            img.style.marginTop = (h - lh) /  + 'px';  //顺手垂直居中
        } else {
            img.width = newImg.width;
            img.height = newImg.height;
            lh = window.ActiveXObject ? parseInt(img.currentStyle['height']) : img.height;
            img.style.marginTop = (h - lh) /  + 'px';  //顺手垂直居中
        }
    } else {
        if (newImg.height > h) {
            img.height = h;
            img.width = newImg.width * h / newImg.height;
        } else {
            img.width = newImg.width;
            img.height = newImg.height;
        }
    }
};