Edit in JSFiddle

<!-- Button to trigger modal -->
<a href="#lazycarouselmodal" role="button" class="btn" data-toggle="modal">Launch lazy carousel</a>
 
<!-- Modal -->
<div id="lazycarouselmodal" class="modal hide fade" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
  <div class="modal-header">
    <button type="button" class="close" data-dismiss="modal" aria-hidden="true">×</button>
    <h3 id="myModalLabel">Lazy Carousel</h3>
  </div>
  <div class="modal-body">
      <div id="ajaxloader">
         <h4> loading images please wait </h4>
         <img src="http://i.imgur.com/m1fR7ef.gif"></img>
      </div> 
    <div id="lazycarousel" class="carousel slide">
  <ol class="carousel-indicators">
    <li data-target="#lazycarousel" data-slide-to="0" class="active"></li>
    <li data-target="#lazycarousel" data-slide-to="1"></li>
    <li data-target="#lazycarousel" data-slide-to="2"></li>
  </ol>
  <!-- Carousel items -->
  <div class="carousel-inner">
    <div class="active item">
        <img data-src="http://24.media.tumblr.com/b273172b94f360682fe9d9b5b78ad672/tumblr_mr80a1mhlR1st5lhmo1_1280.jpg"/>
    </div>
    <div class="item">
        <img data-src="http://24.media.tumblr.com/408fbfeae2d8590512b9fc9cc6207090/tumblr_mr807bH7hh1st5lhmo1_1280.jpg"/>
    </div>
    <div class="item">
        <img data-src="http://31.media.tumblr.com/11d494e09d78f3979af67e256862e85b/tumblr_mr80f71qQe1st5lhmo1_1280.jpg"/>
    </div>
  </div>
  <!-- Carousel nav -->
  <a class="carousel-control left" href="#lazycarousel" data-slide="prev">&lsaquo;</a>
  <a class="carousel-control right" href="#lazycarousel" data-slide="next">&rsaquo;</a>
</div>
  </div>
  <div class="modal-footer">
    <button class="btn" data-dismiss="modal" aria-hidden="true">Close</button>
  </div>
</div>

$('div.modal').on('show', function(e){
    var carousel = $(this).find('.carousel').hide();
    var deferreds = [];
    var imgs = $('.carousel', this).find('img');
    // loop over each img
    imgs.each(function(){
        var self = $(this);
        var datasrc = self.attr('data-src');
        if (datasrc) {
            var d = $.Deferred();
            self.one('load', d.resolve)
                .attr("src", datasrc)
                .attr('data-src', '');
            deferreds.push(d.promise());
        }
    });

    $.when.apply($, deferreds).done(function(){
        $('#ajaxloader').hide();
        carousel.fadeIn(1000);
    });
});