markup.html

<div id="myshow" class="cycle-slideshow" data-cycle-pager="#pager-container">
	<img src="img1.jpg"/>
	<img src="img2.jpg"/>
	<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==" data-img="img3.jpg"/>
	<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==" data-img="img4.jpg"/>
	<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==" data-img="img5.jpg"/>
	<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==" data-img="img6.jpg"/>
</div>
<div id="pager-container"></div>

script.js

$(document).ready(function(){

	$('#myshow').on( 'cycle-before', function(e, optionHash, outgoingSlideEl, incomingSlideEl, forwardFlag ) {
		nextImg = $('#bigshow img').eq(optionHash.nextSlide + 1);
		if ( nextImg.attr("src") == "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw=="){
			nextImg.attr("src", nextImg.attr("data-img"));
		}			
	});
 
});