how to set an image as featured image of a post with php on Wordpress?
As i understand you want to use a image as a featured image on post right ?then why you are not using backend featured image browse option on post. brom there you can simply uplod image as featured and that featured image you can show with this code on your page the_post_thumbnail( $size, $attr );
you need to add the following line at the end of your code :
// add featured image to postadd_post_meta($post_id, '_thumbnail_id', $attach_id);