var b = 1;
var c = true;
$(function(){
    fade();
    
})
//图像渐变
function fade()
{
     if(c == true)
     { 
        b+=2;   
        setTimeout("fade()",3);}
     if(b<99)
     { 
        if(checkFirefoxOrIE())
            $("#img")[0].filters.alpha.opacity=0 + b;
        else
            $("#img")[0].style.opacity=0 + b;
        c == false;
     }
     
}
    

function showRandomImage(){
	var idx = "img"+Math.ceil(Math.random()*16);
	document.write("<img id='img' src='images/"+idx+".jpg' style='width:498px;height:254px;filter:alpha(opacity=0);opacity:0';' />");
}