Yes you can do this on your template's overrides.
Locate this block of code in the item.php file:
<?php if($this->item->params->get('itemImageMainCaption') && !empty($this->item->image_caption)): ?>
<!-- Image caption -->
<div class="itemImageCaption"><?php echo $this->item->image_caption; ?></div>
<?php endif; ?>
And change it to this.
<?php if($this->item->params->get('itemImageMainCaption')): ?>
<!-- Image caption -->
<div class="itemImageCaption"><?php echo $this->item->author->name; ?></div>
<?php endif; ?>
This post will help you locate/ override the item.php file:
getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates 
