To get resized post image you can use next code in your template files:

 <?php
   $width = 100;
   $height = 150;
   $imageHelper = $this->helper(\Magefan\Blog\Helper\Image::class);
 ?>
<img
   src="<?php echo $imageHelper->init($_post->getFeaturedImg())->resize($width, $height); ?>"
   alt="<?php echo $block->escapeHtml($_post->getTitle(), null, true) ?>" />