<?php
    $category = Mage::getSingleton('catalog/layer')->getCurrentCategory();
    $categories = $category->getCollection()
            ->addAttributeToSelect(array('name', 'thumbnail'))
            ->addAttributeToFilter('is_active', 1)
            ->addIdFilter($category->getChildren())
    ?>
    <ul class="subcategories">
        <?php foreach ($categories as $category): ?>
            <li>
                <a href="<?php echo $category->getUrl() ?>"><img src="<?php echo Mage::getBaseUrl('media') . 'catalog' . DS . 'category' . DS . $category->getThumbnail() ?>" alt="<?php echo $this->htmlEscape($category->getName()) ?>" />
                <span><?php echo $category->getName() ?></span></a>
            </li>
        <?php endforeach; ?>
    </ul>

<?php if($category->getThumbnail()): ?>
    <img id="slide-img-1" src="<?php echo $this->helper('catalog/image')->init($category, 'thumbnail')->resize(135, 135); ?>" /></a>
<?php endif; ?>

<?php if($category->getThumbnail()){ ?>
    <img id="slide-img-1" src="<?php echo $this->helper('catalog/image')->init($category, 'thumbnail')->resize(135, 135); ?>" /></a>
   <?php else: ?>
          <img id="slide-img-1" src="placeholderUri" /></a>
<?php endif; ?>