页面图片显示(按比例缩放）

function scaleImage(ImgD, FitWidth, FitHeight){
    var width = ImgD.width, height = ImgD.height;
    var w = width / FitWidth, h = height / FitHeight;
    if (w >= h) { //宽度固定，高度缩放
        ImgD.width = FitWidth;
        ImgD.height= height / w;
        jQuery(ImgD).css("margin-top", (FitHeight-ImgD.height) / 2); //垂直居中
    } else { //高度固定，宽度缩放
        ImgD.height= FitHeight;
        ImgD.width = width / h;			
    }
};

<img src="" onload="scaleImage(this, 100, 80)">