var Move_fn = {};
(function(Move_fn){
    function Move_img() {
        
    }
    Move_img.prototype = {
        constructor:Move_img,
        pageInit: function(imgEle, imgContent) {
            this.Ele = imgEle;
            this.Box = imgContent;
                        imgEle.className = "_positon";//添加定位属性便于计算拖拽位置
            this._mw = imgContent.offsetWidth - imgEle.offsetWidth;
            this._mh = imgContent.offsetHeight - imgEle.offsetHeight;
            this.mouseDown();
            this.closeEvt();
        },
        closeEvt:function() {
            var that = this;
            this.Box.onclick = function(e) {
                e.preventDefault();
                e.stopPropagation();
                if(e.target.tagName == "DIV" || e.srcElement.tagName == "div") {
                    Elf.utils.remove(that.Box.parentNode, that.Box.parentNode.parentNode);
                }
            }
        },
        mouseDown: function() {
            var that = this;
            this.Ele.onmousedown = function(e) {
                that.offX = e.offsetX;
                that.offY = e.offsetY;
                that.mouseMove();
            }
        },
        mouseMove: function(){
            var that = this;
            document.onmousemove = function(e) {
                var l = e.clientX - that.offX;
                var t = e.clientY - that.offY;
                //判断边界设置最大最小值
                if(t <= 0) {
                    t = 0;
                }
                if(t >= that._mh) {
                    t = that._mh;
                }
                if(l <= 0) {
                    l = 0;
                }
                if(l >= that._mw) {
                    l = that._mw;
                }
                that.Ele.style.top = t + "px";
                that.Ele.style.left = l + "px";
                that.mouseUp();
            }
        },
        mouseUp: function() {
            var that = this;
            document.onmouseup = function(e) {
                document.onmousemove = null;
                document.onmousedown = null;
            }
        }
    }
    Move_fn.move_img = new Move_img();
}(Move_fn));

Move_fn.move_img.pageInit(imgShow, imgContent);
初始化一下,要求imgContent全屏遮盖
禁止掉图片自己的拖拽事件,对要拖拽的图片添加几个属性

• oncontextmenu:"false" 禁止图片右键菜单弹出
• onselectstart:"false" 禁止图片选中
• ondragstart:"false" 禁止图片拖拽
• draggable:"false" 禁止图片拖拽