If you mean the intro image that's used in intro_image layout, use the same check as in the layout:

    <?php $images = json_decode($this->item->images); ?>
    <?php if (isset($images->image_intro) && !empty($images->image_intro)) : ?>
        <div><?php echo $this->item->introtext; ?></div>
    <?php else : ?>
        <?php echo $this->item->introtext; ?>
    <?php endif; ?>