function picresize(obj,MaxWidth,MaxHeight){
    obj.onload=null;
    img=new Image();
    img.src=obj.src;
    if (img.width>MaxWidth && img.height>MaxHeight){
        if (img.width/img.height>MaxWidth/MaxHeight) {
            obj.height=MaxWidth*img.height/img.width;
            obj.width=MaxWidth;
        }else {
            obj.width=MaxHeight*img.width/img.height;
            obj.height=MaxHeight;
        }
    }else if (img.width>MaxWidth) {
        obj.height=MaxWidth*img.height/img.width;
        obj.width=MaxWidth;
    }else if (img.height>MaxHeight) {
        obj.width=MaxHeight*img.width/img.height;
        obj.height=MaxHeight;
    }else{
        obj.width=img.width;
        obj.height=img.height;
    }
}