, поставив

			<div class="image cell">
				<input type=hidden name=purchases[id][{$purchase->id}] value='{$purchase->id}'>
				{$image = $purchase->product->images|first}
				{if $image}
				<a href="{$image->filename|resize:800:600}" class="zoom" rel="group"><img src="{$image->filename|resize:50:50}" alt="{$product->product->name|escape}" /></a>
				{/if}
			</div>

class="zoom" rel="group" подключает fancibox , а resize:800:600 устанавливает размеры картинок.