WordPress function; As it is important for a11y (accessibility) that images got an ALT text this function adds, on upload, the IPTC description from the image to the "Alternative Text" field within WordPress.

wordpress-auto-add-alttext-on-upload.php

/* Automatically set an image Alt-Text on upload */
add_action( 'add_attachment', 'kreks__add_alt_text_from_image_IPTC_on_upload' );

function kreks__add_alt_text_from_image_IPTC_on_upload( $post_ID ) {
	// Check if uploaded file is an image, else do nothing
	if ( wp_attachment_is_image( $post_ID ) ) {
		$postMeta = get_post_meta($post_ID);
		$uploads = wp_get_upload_dir();
		$imgURL = $uploads['basedir'] . "/" . $postMeta['_wp_attached_file']['0'];

		$size = getimagesize( $imgURL, $imageInfo );
		$iptc = iptcparse($imageInfo['APP13']);
		$description = $iptc["2#120"][0];

		// Set the image Alt-Text
		update_post_meta( $post_ID, '_wp_attachment_image_alt', $description );
	}
}