wp-update-image-alt-tags-on-upload-from-filename

wp-update-alt-tags-on-upload.php

<?php
add_action( 'add_attachment', 'update_image_alt_tags_on_upload' );

function update_image_alt_tags_on_upload( $post_ID ) {

	if ( wp_attachment_is_image( $post_ID ) ){
		$image_name = get_post( $post_ID )->post_title;
		$image_name = preg_replace( '%\s*[-_\s]+\s*%', ' ', $image_name ); // Replace '-''_' with single space
		$image_name = ucwords( strtolower( $image_name ) ); // Capitalize first letter
		
		update_post_meta( $post_ID, '_wp_attachment_image_alt', $image_name );
		
		}
}