Set Image Caption via PHP in WordPress

In order to change an image’s caption, you can of course find that image in the WordPress Media Gallery and enter a new value in the Caption field, but what if you want to update the captions of 100 images? It’d be much more efficient to write some code to handle that for you.

As an example, here’s how you would set the captions of a few images to be the same as the image title:

// The IDs of the posts for which you want to update the featured image caption
$post_ids_to_update = array( 21, 57, 95 );

// Loop through each of the post IDs
foreach ( $post_ids_to_update as $post_id ) {

	// Get the ID of this post's featured image
	$featured_image_id = get_post_thumbnail_id( $post_id );

	// Get the title of this post's featured image
	$featured_image_title = get_the_title( $featured_image_id );

	// Sanitize the text so we're ready to insert it into the database
	$new_caption_text = sanitize_text_field( $featured_image_title );

	// Set the new caption (a.k.a. the post excerpt) of the featured image
	wp_update_post( 'post_excerpt', $featured_image_title )
}