jquery.lazyloading.js的作用/加载过程/原理/设计思路：
1、刚加载页面时只加载html,不加载图片，图片的src为空，把真实的图片路径放到data-original属性中，页面加载速度变快；
2、在页面加载完成之后，js初始化，把有data-original属性的图片再加一个<div></div>在外面，再创建一个隐藏的<img />标签，并且根据原图片的大小和位置计算loading图片的位置，把loading图片显示在中间；
3、判断window的scroll事件（滚动条变化），判断图片在不在可视区域内，如果在可视区域内，那么执行第4步，否则什么也不做。
4、判断图片的src与data-original是不是相同，如果不相同（说明还没有加载），执行第5步，否则什么也不做。
5、把图片的data-original赋值给隐藏的<img />标签的src，当隐藏的图片完全加载好之后（完成后会执行它的.load()事件），再把隐藏图片的src赋值给原图片的src(原因：保证loading图片消失后目标图片立即显示，如果一开始把data-original赋值给图片的src，那么还没加载完就会显示图片，网页中图片是一截一截显示的，非常难看).

（为了保证在火狐中，图片未加载或图片路径不对，图片的位置被其他元素占用），请不要写.lazyloading的css样式，否则页面会乱。

通用的图片的html：

<div style="width: 772px; height: 449px;">
   <img class="lazyloading" src="" data-original="/ListPicThumbnail/list90.jpg" height="772" width="449">
</div>
或者l：

<div style="width: 772px; height: 449px;">
   <a href="#" target="_blank"> <img class="lazyloading" src="" data-original="/ListPicThumbnail/list90.jpg" height="772" width="449"> </a>
</div>

不断修改完善中……

最后更新：2013-12-17 16:00:00

加载等的图片：

/*!
* jquery.lazyoading.js
*自定义的页面图片延迟加载插件，比网上的jquery.lazyload简单，也更适合自己的网站
*使用方法：
把img 的class加上 lazyloading,data-original 放图片的真实路径
然后先引用jquery，再引用jquery.lazyoading.js，再调用：$("img.lazyloading").lazyloading({loadfirst:true});
* by pukuimin
* 2013-11-01
*2013-11-08 解决了图片没有指定高度的问题
*2013-11-14 解决了没有指定高度加载图片之后有间隔的问题
*2013-12-17 加入了<span>图片显示时的 animate过渡效果</span>，把alt赋值给title
 */
/// <reference path="jquery-1.8.2.min.js" />
(function ($) {
    $.fn.lazyloading = function (options) {
        var defaults = {
            preyimg: "/Content/images/Imgpreview/grey.gif",
            picpath: "data-original",
            container: $(window),
            loadfirst: false, //进入页面后是否加载当前页面的图片
            defaultHeightID: "lazyloadingHeight"//页面上默认高度的input标签id
            //imgPaddingID: "lazyloadingPadding"//img的padding值
        };
        var params = $.extend({}, defaults, options || {});
        params.cache = [];
        $(this).each(function () {
            var node = this.nodeName.toLowerCase(), url = $(this).attr(params["picpath"]), preyimg = params["preyimg"];
            var defaultheight = $("#" + params["defaultHeightID"]).val(); //, padding = $("#" + params["imgPaddingID"]).val(); //
            //重组
            var data = {
                obj: $(this),
                tag: node,
                url: url,
                preyimg: preyimg,
                defaultheight: defaultheight
            };
            params.cache.push(data);
        });

        var init = function () {
            $.each(params.cache, function (i, data) {
                var thisImg = data.obj, tag = data.tag, url = data.url, preyimg = data.preyimg;
                if (typeof (url) != "undefined")// 判断是否需要延迟加载
                {
                    var parent1 = thisImg.parent(); //a
                    var Inner = null; //
                    if (parent1.is("a") == true) {//img wrap by a
                        Inner = parent1;
                    }
                    else {
                        Inner = thisImg;
                    }
                    var width = thisImg.attr("width") || thisImg.css("width");
                    var height = data.defaultheight || thisImg.css("height");
                    //if (i == 0) alert(data.defaultheight);
                    var attrheight = thisImg.attr("height");
                    if (attrheight != null) height = attrheight;
                    if (width != null && width.indexOf("px") > -1) width.replace("px", "");
                    if (height != null && height.indexOf("px") > -1) height.replace("px", "");
                    var divstr = "<div class='.loading' style='text-align: left;position:relative;float:left;width:" + width + "px;";
                    var HasHeight = true; //图片是否指定了高度
                    divstr = divstr + "height:" + height + "px;";
                    if (attrheight == null || attrheight == "") {
                        HasHeight = false;
                    }

                    thisImg.css("position", "relative");

                    divstr = divstr + "' ></div>"
                    //修正外层div：text-align的影响
                    Inner.wrap(divstr);
                    //修正img外面不是a标签时parent()已经改变的问题
                    parent1 = thisImg.parent();
                    if (HasHeight == true) { parent1.attr("lazyloading_hasheight", "1"); } //是否指定了高度
                    else { { parent1.attr("lazyloading_hasheight", "0"); } }
                    parent1.append("<img class='loadhiddenimg' width='0' height='0' style='display:none;' src='' />");
                    thisImg.attr("src", preyimg);
                    thisImg.removeAttr("width").removeAttr("height");
                    thisImg.attr("width1", width).attr("height1", attrheight);

                    ////thisImg.attr("width", "50px").attr("height", "50px"); //loading图大小
                    //thisImg.css("margin", "0 auto");
                    thisImg.css("margin", ((height / 2) - 25) + "px auto auto " + ((width / 2) - 25) + "px");
                    $(".lazyloading").css("display", "table"); //.css("position", "relative");
                }
            });
        }
        //动态显示数据
        var loading1 = function () { };
        var loading = function () {
            //窗口的高度+看不见的顶部的高度=屏幕低部距离最顶部的高度
            var thisButtomTop = parseInt($(window).height()) + parseInt($(window).scrollTop());
            var thisTop = parseInt($(window).scrollTop()); //屏幕顶部距离最顶部的高度

            $.each(params.cache, function (i, data) {
                var thisImg = data.obj, tag = data.tag, url = data.url, post, posb;

                if (thisImg) {//对象不为空
                    if (typeof (url) != "undefined") {// 判断是否需要延迟加载
                        var PictureTop = parseInt(thisImg.offset().top);
                        //如果处理可见范围内，并且原图地址data-original不等于src,则加载图片
                        if (PictureTop >= thisTop && PictureTop <= thisButtomTop && thisImg.attr("data-original") != thisImg.attr("src")) {
                            var hiddenImg = thisImg.siblings("img.loadhiddenimg");

                            hiddenImg.load(function () { //隐藏图片加载完之后的回调函数
                                var width = thisImg.attr("width1");
                                var height = thisImg.attr("height1");
                                thisImg.attr("width", width).attr("height", height).removeAttr("width1").removeAttr("height1");
                                thisImg.css("margin", "0 auto");
                                if (thisImg.parent().attr("lazyloading_hasheight") == "0") {//没有指定高度时，加载图片后去掉div高度自适应
                                    if (thisImg.parent().is("a") == true) {
                                        thisImg.parent().parent().css("height", "");
                                    }
                                    else {
                                        thisImg.parent().css("height", "");
                                    }
                                }
                                thisImg.load(function () {
                                    if (thisImg.parent().is("a") == true) {
                                        thisImg.parent().parent().css("height", thisImg.height());
                                    }
                                    else {
                                        thisImg.parent().css("height", thisImg.height());
                                    }
                                });
                                thisImg.css('opacity', '0.2');
                                thisImg.attr("src", hiddenImg.attr("src"));
                                thisImg.animate({ opacity: 1.0 });
                                if (thisImg.attr("alt") != "") {
                                    thisImg.attr("title", thisImg.attr("alt"));
                                    thisImg.attr("alt", "");
                                }
                            }).error(function () {
                                thisImg.error(function () {
                                    thisImg.css("margin", "0 auto auto 0");
                                    if (thisImg.parent().attr("lazyloading_hasheight") == "0") {//没有指定高度时，加载图片后去掉div高度自适应
                                        if (thisImg.parent().is("a") == true) {
                                            thisImg.parent().parent().css("height", "");
                                        }
                                        else {
                                            thisImg.parent().css("height", "");
                                        }
                                    }
                                });
                                thisImg.attr("src", hiddenImg.attr("src")); //alert("error");
                                if (thisImg.attr("alt") != "") {
                                    thisImg.attr("title", thisImg.attr("alt"));
                                    thisImg.attr("alt", "");
                                }
                            });
                            hiddenImg.attr("src", url);
                        }
                    }
                }
            });
        };
        //初始化
        init();
        //事件触发
        //加载完毕即执行
        if (params["loadfirst"] == true) loading();
        //滚动执行
        params.container.bind("scroll", loading).bind("resize", loading);
    };
})(jQuery);

用法示例：

<div style="width: 190px; height: 237px; float: left;"><a href="http://maga.kinpan.com/Magazine/MagazineEachperiod/sdlp?id=201311011146457968750c36ca60628">
  <img  alt="商业街区" src="" data-original="http://account.kinpan.com/Upload/Magazine/MagazineBookImage/201311011141232812500a4cbf15f0f.jpg" width="190" height="237" class="lazyloading" /></a>
</div>

<script type="text/javascript">

$(function () {

    $("img.lazyloading").lazyloading({ loadfirst: true });

})

</script>

使用本插件有任何问题可以一起交流，我的常用邮箱：pukuimin@qq.com