You are using $post_id
, but you have passed the post ID as $postID
. As a result $a
is always empty.
Even if it weren’t empty, there is no PHP function srtpos
. It’s strpos
and you could have more straightforward logic to execute set_post_format
.
Wrapping it up:
function CambiarPostFormat( $postID ) {
$a = get_the_title( $postID );
if ( !has_post_format( 'image', $postID ) && strpos($a, 'imagenes') !== false)
set_post_format( $postID, 'image' );
}