I've found a possible solution. Maybe it's quite a trick, but it works.
Since K2 doesn't store the path to the image into the database, I've used other fields that are stored. In particular, I've used the image_credits field.
In that field I insert the path to the image (/images/myimage.jpg) that I've uploaded on the server via ftp or via any other means that allow you to upload a picture into the image folder.
Now I've made some minor modifications into the template overrides of the item, adding an else branch to the if that manage the image
<?php else:
if(!empty($this->item->image_credits)): ?>
<figure class="itemImageBlock">
<a class="itemImage modal" rel="{handler: 'image'}" href="<?php echo $this->item->image_credits; ?>" title="<?php echo JText::_('K2_CLICK_TO_PREVIEW_IMAGE'); ?>">
<img src="<?php echo $this->item->image_credits; ?>" alt="<?php if(!empty($this->item->image_caption)) echo K2HelperUtilities::cleanHtml($this->item->image_caption); else echo K2HelperUtilities::cleanHtml($this->item->title); ?>" style="width:100%; height:auto;" />
</a>
</figure>
<?php endif; ?>That's it. Now I can "translate" the image using Joomfish
