If you are looking at how to insert a featured image inside a post, you can try the following solution.
Add the following code inside the functions.php of your theme:
add_shortcode('thumbnail','thumbnail_in_content'); function thumbnail_in_content( $atts ) { global $post; return get_the_post_thumbnail( $post->ID ); }
Control the features images with the shortcode:
[thumbnail size=medium align=right]
The side can be changed to small, medium and large values and/or align can be none, center, right or left.
Another way to control the thumbnail size with size=’array( 300, 200)’. It will look like this
[thumbnail size='array( 300, 200)']
Change the array value to a different number to achieve the result you need.