WordPress at a glance
filter is not described

image_add_caption_text filter-hook . WP 4.1.0

Filters the caption text.

Note: If the caption text is empty, the caption shortcode will not be appended to the image HTML when inserted into the editor.

Passing an empty value also prevents the 'image_add_caption_shortcode' Filters from being evaluated at the end of image_add_caption().

Usage

add_filter( 'image_add_caption_text', 'filter_function_name_3951', 10, 2 );
function filter_function_name_3951( $caption, $id ){
	// filter...

	return $caption;
}
$caption(string)
The original caption text.
$id(int)
The attachment ID.

Where the hook is called

image_add_caption()
wp-admin/includes/media.php 188
$caption = apply_filters( 'image_add_caption_text', $caption, $id );

Where the hook is used (in WP core)

Does not used.