img {
	display:none;
	border: none;
}


.large{
	display:compact;
	width:300px;
	height:auto;
}
	
	

<div class="popimg"><a href="#" title="" class="popup">
	<img src="bikes.jpg" width="37" height="25" alt="バイク" title="バイク" />
<img src="pictures/bikes.jpg" width="500" height="374" alt="バイク" title="バイク" class="large" /></a>
</div>