WordPress at a glance
filter is not described

the_post_thumbnail_caption filter-hook . WP 4.6.0

Filters the displayed post thumbnail caption.

Usage

add_filter( 'the_post_thumbnail_caption', 'filter_function_name_578' );
function filter_function_name_578( $caption ){
	// filter...

	return $caption;
}
$caption(string)
Caption for the given attachment.

Where the hook is called

the_post_thumbnail_caption()
wp-includes/post-thumbnail-template.php 258
echo apply_filters( 'the_post_thumbnail_caption', get_the_post_thumbnail_caption( $post ) );

Where the hook is used (in WP core)

wp-includes/default-filters.php 174
add_filter( 'the_post_thumbnail_caption', 'wptexturize' );
wp-includes/default-filters.php 175
add_filter( 'the_post_thumbnail_caption', 'convert_smilies' );
wp-includes/default-filters.php 176
add_filter( 'the_post_thumbnail_caption', 'convert_chars' );