You can edit file templates/jf_salina/html/com_k2/portfolio-masonry/item.php, add code to below the tags (may be at line 178):
<?php if($this->item->params->get('itemImage') && !empty($this->item->image)): ?>
<!-- Item Image -->
<div class="itemImageBlock">
<span class="itemImage">
<img src="<?php echo $this->item->image; ?>" alt="<?php if(!empty($this->item->image_caption)) echo K2HelperUtilities::cleanHtml($this->item->image_caption); else echo K2HelperUtilities::cleanHtml($this->item->title); ?>" style="width:<?php echo $this->item->imageWidth; ?>px; height:auto;" />
</span>
<?php if($this->item->params->get('itemImageMainCaption') && !empty($this->item->image_caption)): ?>
<!-- Image caption -->
<span class="itemImageCaption"><?php echo $this->item->image_caption; ?></span>
<?php endif; ?>
<?php if($this->item->params->get('itemImageMainCredits') && !empty($this->item->image_credits)): ?>
<!-- Image credits -->
<span class="itemImageCredits"><?php echo $this->item->image_credits; ?></span>
<?php endif; ?>
<div class="clr"></div>
</div>
<?php endif; ?>
joomfreak