This works for what you are trying to accomplish in your code:
jsfiddle example: http://jsfiddle.net/larryjoelane/gz4gst49/14/
With the code below placed in a script tag at the bottom of your body document you 
still use the alert if you want:
<script>
//the class to click on
var selector = ".center-block";
//set the doubleClicked variable to 0 meaning false
//in this example
var doubleClicked = 0;
//on single click function for selector class
$(selector).on("click",function(){//begin function
//use time out function to delay execution for specified amount
//of time in this case I used 2 seconds
setTimeout(function () {
    //if doubleClicked equals 0
    if (doubleClicked === 0){//begin if then
            //display alert
            alert("hello");
    }//end if then else
    }, 2000);//<--delay set for two seconds
});//end function
//on double click function
$(selector).on("dblclick",function(){//begin function
    //set doubleClicked to 1 
    doubleClicked = 1;
    //remove the img element
    $("img").remove();
});//end function
 </script>