//定义鼠标拖动对象
drag=function (a,o){
var d=document;if(!a)a=window.event;
if(!a.pageX)a.pageX=a.clientX;
if(!a.pageY)a.pageY=a.clientY;
var x=a.pageX,y=a.pageY;
if(o.setCapture)
o.setCapture();
else if(window.captureEvents)
window.captureEvents(Event.MOUSEMOVE|Event.MOUSEUP);
var backData = {x : o.style.top, y : o.style.left};
d.onmousemove=function(a){
if(!a)a=window.event;
if(!a.pageX)a.pageX=a.clientX;
if(!a.pageY)a.pageY=a.clientY;
var tx=a.pageX-x+parseInt(o.style.left),ty=a.pageY-y+parseInt(o.style.top);
o.style.left=tx+"px";
o.style.top=ty+"px";
x=a.pageX;
y=a.pageY;
};
d.onmouseup=function(a){
if(!a)a=window.event;
if(o.releaseCapture)
o.releaseCapture();
else if(window.captureEvents)
window.captureEvents(Event.MOUSEMOVE|Event.MOUSEUP);
d.onmousemove=null;
d.onmouseup=null;
if(!a.pageX)a.pageX=a.clientX;
if(!a.pageY)a.pageY=a.clientY;
if(!document.body.pageWidth)document.body.pageWidth=document.body.clientWidth;
if(!document.body.pageHeight)document.body.pageHeight=document.body.clientHeight;
if(a.pageX < 1 || a.pageY < 1 || a.pageX > document.body.pageWidth || a.pageY > document.body.pageHeight){
o.style.left = backData.y;
o.style.top = backData.x;
}
};
}

<div id="divPhoto" onmousedown="drag(event,this)"></div>