Manipulates the metadata for uploaded images at upload time to make better use of IPTC data that may be present.

image_meta.php

<?php 
/*
	
Manipulates the metadata for uploaded images at upload time to make better use
of IPTC data that may be present.

An image is stored as an attachment, which is a special type of post. It is 
handled the same way as any other post type.

As far as the meta goes, it's stored like this:

Image title is stored as post_title in wp_post, 
Description is stored as post_content in wp_post, 
Caption is stored as post_excerpt in wp_post
Alt Text is stored as _wp_attachment_image_alt in wp_postmeta
The rest of the meta data is stored as _wp_attachment_metadata as aa serialized 
  entry in wp_postmeta

When reading meta from the file during ingest, WP uses the following as its source,
in order of appearance:

Title:
1. IPTC:Headline
2. IPTC:Title
3. IPTC:Description if less than 80 characters
4. EXIF:Title (which doesn't actually exist)
5. EXIF:ImageDescription if less than 80 characters
6. Filename minus extension

Caption:
1. IPTC:Description
2. EXIF:UserComment if title is unset AND EXIF:ImageDescription is less than 80 characters
3. EXIF:ImageDescription if title is set OR EXIF:ImageDescription is more than 80 characters
4. EXIF:Comments if title !== EXIF:Comments
	1. Image title = IPTC Headline
	2. Image description = IPTC Description

Alt Text:
none

Description:
1. IPTC:Description if more than 80 characters


What this code does is the following:
	1. Image title = IPTC Title if present, even if IPTC:Headline is set
	2. Image caption = IPTC Headline
	3. Image alt text = Image Caption (done is step 2) + comma-separated IPTC:Keywords
	4. Image Description = IPTC:Description regardless of length
	5. Add a new meta value called md_meta_update_complete to track whether these
	     adjustments have been done.

We can't do this at metadata collection time (such as by hoooking into 
wp_read_image_metadata)because some of this info is stored as wp_post 
and the entry doesn't exist at the time wp_read_image_metadata is running.


Logic Steps
	1. Copy Title (post_title) to Caption (post_excerpt). Refer to default logic
	    above to understand why this is valid
	2. If IPTC:Title, set Title (post_title) to IPTC:Title
	3. Read in the IPTC Keywords and insert into Alt along with Caption
	4. Readin IPTC:Description and insert into description (post_content)

*/

// Hook into add_attachment at the very end
add_filter('add_attachment', 'md_force_image_metadata', 99, 2);

/*******************************************************************************
	Wrapper to call the steps in order.
	@param int 		$image_id, attachment ID
	@return none
*/
function md_force_image_metadata( $image_id ) {
	$image_meta = wp_get_attachment_metadata( $image_id );

	// Only run if it hasn't already been run
	if ( ! isset($image_meta['md_meta_update_complete']) || ! $image_meta['md_meta_update_complete'] ) {

		//	1. Copy Title (post_title) to Caption (post_excerpt)
		md_copy_title_to_caption( $image_id );
	
		// 2. Read in the IPTC:Title from the file and insert into post_title
		md_insert_IPTC_title_as_title( $image_id );
	
		// 3. Read in the IPTC:Keywords from the file and insert into Alt
		md_insert_IPTC_keywords_as_alt( $image_id );

		// 4. Read in IPTC:Description and put it into description (post_content)
		md_insert_IPTC_description_as_description( $image_id );
	
		// 5. Insert the flag to indicate we're done
		$image_meta = wp_get_attachment_metadata( $image_id );
		$image_meta['md_meta_update_complete'] = true;
		update_post_meta($image_id, '_wp_attachment_metadata', $image_meta);
	}
}


/*******************************************************************************
	By default, the IPTC:Description is used as the title if it's less than 80
	characters long, which means that description would be empty. This forces
	description to be IPTC:Description no matter how long it is. Overwrites 
	existing description if present.	

	@param int 		$image_id, attachment ID
	@return none

*/
function md_insert_IPTC_description_as_description( $image_id ) {
	if ( wp_attachment_is_image( $image_id ) ) {
		$desc = md_get_iptc_tag( $image_id, 'Description');
		md_log( "Desc is $desc" );
		if ( $desc ) {
			// Update the post_content, which is used for the description
			$updated_post = array(
				'ID'	=> $image_id,
				'post_content' =>  $desc,
			);
			wp_update_post( $updated_post );
		}
	}
}



/*******************************************************************************
	Copies the image title (post_title) WP did on its own (and used IPTC Headline 
	for) and copies into the caption (post_excerpt). Overwrites existing caption, 
	but at ingest time it'll be blank so who cares.	

	@param int 		$image_id, attachment ID
	@return none

*/
function md_copy_title_to_caption( $image_id ) {
	if ( wp_attachment_is_image( $image_id ) ) {
		$image_obj = get_post( $image_id );
		$image_meta = wp_get_attachment_metadata( $image_id );

		// First update the image meta
		$image_meta['image_meta']['caption'] = $image_obj->post_title;
		update_post_meta($image_id, '_wp_attachment_metadata', $image_meta);

		// Then update the post_excerpt, which is used for the caption
		$updated_post = array(
			'ID'	=> $image_id,
			'post_excerpt' =>  $image_obj->post_title,
		);
		wp_update_post( $updated_post );
	}
}


/*******************************************************************************
	Inserts IPTC title as image title (post_title). Overwrites 
	existing title.	

	@param int 		$image_id, attachment ID
	@return none
*/
function md_insert_IPTC_title_as_title( $image_id ) {
	if ( wp_attachment_is_image( $image_id ) && is_callable( 'iptcparse' ) ) {
		$title = '';
		$title = md_get_iptc_tag( $image_id, 'Title');
		if ( $title ) {
		// First update the image meta
			$image_meta = wp_get_attachment_metadata( $image_id );
			$image_meta['image_meta']['title'] = $title;
			update_post_meta($image_id, '_wp_attachment_metadata', $image_meta);
			
			// Then update the post_title
			$updated_post = array(
				'ID'	=> $image_id,
				'post_title' =>  $title,
			);
			wp_update_post( $updated_post );
		}
	}
}


/*******************************************************************************
	Inserts caption and IPTC keywords as comma separated string into Alt Text.
	Overwrites existing Alt Text, but at ingest time it'll be blank so who cares.	

	@param int 		$image_id, attachment ID
	@return none

*/
function md_insert_IPTC_keywords_as_alt( $image_id ) {
	if ( wp_attachment_is_image( $image_id ) && is_callable( 'iptcparse' ) ) {
		$keywords = md_get_iptc_tag( $image_id, 'Keywords');
		$image_meta = wp_get_attachment_metadata( $image_id );
		$caption = $image_meta['image_meta']['caption'];
		if ( $caption ) { $caption .= "; ";}
		if ( $keywords || $caption ) {
			update_post_meta($image_id, '_wp_attachment_image_alt', "$caption $keywords");
		}
	}
}


/*******************************************************************************
	Does the actual getting of the IPTC info from the file.

	@param int 		$image_id, attachment ID
	@param string 	$iptc_tag, tag to get, either 'Keywords' or 'Title' or 'Description'
	@return string 	if tag is found and has contents, those contents; empty string otherwise
*/
function md_get_iptc_tag( $image_id, $iptc_tag ) {
	$tag = null;
	$file = get_attached_file( $image_id );
	if ( ! file_exists( $file ) ) { return null; }
	
	// Based on code in image.php in wp core
	$size = getimagesize( $file, $info );
	if ( ! empty( $info['APP13'] ) && ( 'Title' === $iptc_tag || 'Keywords' === $iptc_tag || 'Description' === $iptc_tag ) ) {
		$iptc = iptcparse( $info['APP13'] );
		// User var_dump on $iptc to see everything
		switch ( $iptc_tag ) {
			case 'Title':
				if ( ! empty( $iptc['2#005'][0] ) ) {
					// string
					$tag = trim( $iptc['2#005'][0] );
				}
				break;
			case 'Keywords':
				if ( ! empty( $iptc['2#025'][0] ) ) {
					// array
					$tag = implode( ', ', $iptc['2#025'] );
				}
				break;
			case 'Description':
				if ( ! empty( $iptc['2#120'][0] ) ) {
					// string
					$tag = trim( $iptc['2#120'][0] );
				}
				break;
			default:
		}
	}
	return $tag;	
}