Backbone Template

Standard fiddle

HTML

<ul id="imgs">
</ul>
<p id="output"></p>

JavaScript

var PhotoSrcArray = [];

for(var i = 1; i < 721; i++){
   PhotoSrcArray.push("http://pokedream.com/pokedex/images/blackwhite/front/"+("000" + i).slice(-3)+".png")
}


for(var i = 0; i < PhotoSrcArray.length; i++){
    $("#imgs").append('<li><label><input type="checkbox"></input><img src="'+PhotoSrcArray[i] + '" data-index="'+(i+1).toString() + '"/></label></li>');
}

var myArray = [];

$("li input").change(function(event){
        if (this.checked){
           myArray.push($(event.currentTarget).next('img').attr('data-index')); 
        }
        else {
     var indexOfPhoto = myArray.indexOf($(event.currentTarget).next('img').attr('data-index'));
            if (indexOfPhoto > -1){
                myArray.splice(indexOfPhoto, 1);
            }
        }
        myArray.sort();
        $("#output").html( myArray.join(' '));
//or alert it if you'ld like
});