A simple wrapper function to make retrieving information about a WordPress attachment nicer.

allib-get-image-info.php

<?php
/* Retrieve information about WordPress images without the chaos.

You have to remember a bunch of different functions to get info about images in the
Media Library so I collected their functionality under one wrapper with a (hopefully)
nice interface. This function tries to avoid fetching unnecessary info whenever it can.

I have limited the granularity of the API to not allow fetching different info
about each available image size. I think that would make using this function
more fiddly without any great benefit.

Doing this:

	$image_info = allib_get_image_info(array(
		// The Post ID of the image attachment
		'id' => 687, // REQUIRED
		// You can ask for any combination of the default image sizes (thumbnail, medium, large, full)
		// or any sizes you have defined yourself using add_image_size()
		'sizes' => array('thumbnail', 'medium', 'large', 'full'), // OPTIONAL, defaults to 'thumbnail'

		// Only the info you ask for here will be returned
		'info' => array( // OPTIONAL (but calling this function without it is pointless)

				// url, width, height are retrieved for each size you specified in 'sizes'
				'url', // The full URL to the file
				'width', // Width of the image in pixels
				'height', // Height of the image in pixels

				// Attachment Metadata
				'caption',
				'description',
				'title',
				'alt_text',

				// The URL of the attachment page - the format of this depends on
				// your permalink structure
				'attachment_page_url',

				// This retrieves whatever metadata WordPress was able to extract from
				// the image file itself. It can include info such as shutter speed etc.
				// Confusingly wp_get_attachment_metadata() returns this info and not the
				// caption, description, title, alt-text.
				'image_meta'
				)
	));
	print_r($image_info);

Returns this:
	Array
	(
	    [sizes] => Array
	        (
	            [thumbnail] => Array
	                (
	                    [url] => http://localhost/sandbox/wordpress-stable/wp-content/uploads/2011/12/Kelly_20110127_11847-150x150.jpg
	                    [width] => 150
	                    [height] => 150
	                )

	            [medium] => Array
	                (
	                    [url] => http://localhost/sandbox/wordpress-stable/wp-content/uploads/2011/12/Kelly_20110127_11847-300x188.jpg
	                    [width] => 300
	                    [height] => 188
	                )

	            [large] => Array
	                (
	                    [url] => http://localhost/sandbox/wordpress-stable/wp-content/uploads/2011/12/Kelly_20110127_11847-1024x643.jpg
	                    [width] => 500
	                    [height] => 313
	                )

	            [full] => Array
	                (
	                    [url] => http://localhost/sandbox/wordpress-stable/wp-content/uploads/2011/12/Kelly_20110127_11847.jpg
	                    [width] => 4078
	                    [height] => 2563
	                )

	        )

	    [title] => Kelly_20110127_11847
	    [caption] =>
	    [description] =>
	    [alt_text] =>
	    [image_meta] => Array
	        (
	            [aperture] => 3.5
	            [credit] =>
	            [camera] => NIKON D7000
	            [caption] =>
	            [created_timestamp] => 1296158616
	            [copyright] => Eoin Kelly
	            [focal_length] => 18
	            [iso] => 10000
	            [shutter_speed] => 0.01
	            [title] =>
	        )

	    [attachment_page_url] => http://localhost/sandbox/wordpress-stable/?attachment_id=687
	)

        @version 2012-04-13

	TODO
		*	I just return false on errors - better way to do this? do any of the funcitons I call do different?
		*	research how WP passes variables and validates them in functions - can I do this better?
*/

function allib_get_image_info($args = array()) {

	if (count($args) == 0) {
		return false;
	}

	// We cannot continue if we don't get $id, $requested_info
	$id = (array_key_exists('id', $args)) ? $args['id'] : false;
	$requested_info = (array_key_exists('info', $args)) ? $args['info'] : false;

	// Return false if we don't have the arguments we need
	if (! ($id || $requested_info)) {
		return false;
	}

	// If size not specified, it defaults to 'thumbnail'
	$sizes = (array_key_exists('sizes', $args)) ? $args['sizes'] : array('thumbnail');

	// Initialize a container for our results
	$results = array();

	/*
	 *	If we are asked for any of url, width, height we fetch
	 *	all of them as it is the same function call.
	 */
	if (in_array('url', $requested_info) ||
		in_array('width', $requested_info) ||
		in_array('height', $requested_info)) {

		foreach ($sizes as $size) {
			$a = wp_get_attachment_image_src($id, $size);

			if (in_array('url', $requested_info)) {
				$results['sizes'][$size]['url'] = $a[0];
			}
			if (in_array('width', $requested_info)) {
				$results['sizes'][$size]['width'] = $a[1];
			}
			if (in_array('height', $requested_info)) {
				$results['sizes'][$size]['height'] = $a[2];
			}
		}
	}

	// If we are asked for any of title, description, caption, alt-text, image_meta
	// we need to query the DB
	if (in_array('title', $requested_info) ||
		in_array('description', $requested_info) ||
		in_array('caption', $requested_info) ||
		in_array('image_meta', $requested_info) ||
		in_array('alt_text', $requested_info)) {

		$query = new WP_Query(array(
				'post_type' => 'attachment',
				'p' => $id // Because we specify the id we *should* get 0 or 1 results
		));

		// If we didn't get exactly one result, we return false lest we do harm.
		if (count($query->posts) != 1) {
			return false;
		}

		foreach ($query->posts as $post) {
			if (in_array('title', $requested_info)) {
				$results['title'] = $post->post_title;
			}
			if (in_array('caption', $requested_info)) {
				$results['caption'] = $post->post_excerpt;
			}
			if (in_array('description', $requested_info)) {
				$results['description'] = $post->post_content;
			}
			if (in_array('alt_text', $requested_info)) {
				// get_post_meta() touches the DB again so we only run this function if we have
				// been specifically asked for alt_text
				$results['alt_text'] = get_post_meta($post->ID, '_wp_attachment_image_alt', true);
			}
			if (in_array('image_meta', $requested_info)) {

				// get_post_meta() touches the DB again so we only run this function if we have
				// been specifically asked for image_meta
				$misc_attachment_metadata = get_post_meta( $post->ID, '_wp_attachment_metadata', true );

				if (count($misc_attachment_metadata['image_meta']) > 0) {
					$results['image_meta'] = $misc_attachment_metadata['image_meta'];
				} else {
					$results['image_meta'] = false;
				}
			}
		}
	}

	if (in_array('attachment_page_url', $requested_info)) {
		// get_attachment_link() returns the URI
		// wp_get_attachment_link() returns an HTML hyperlink tag
		$results['attachment_page_url'] = get_attachment_link($id);
	}

	// Return an array if we found any results, otherwise return false
	// as this seems to be the WordPress way(TM).
	if (count($results) > 0) {
		return $results;
	} else {
		return false;
	}
}