In case you need to add image sources yourself, like for images in custom fields, you can use the following filters (see the WordPress Plugin API for information on how to use filter).
isc_images_in_posts
Is applied for the images that are belonging to a post and saved as a meta field to it. This information is used when listing images for single posts and pages. $image_urls contains an array with other arrays for each post. Each looks similar to this example: ‘thumbnail’ is preserved for the post thumbnail. You probably won’t need it.
{attachment_id} => array('src' =>; 'http://example.com/wp-content/uploads/2011/01/example-image.png'
'thumbnail' => 1
)
From the following call of the filter you can see, that the post ID is submitted in case you need it. Use add_filter() like described on the Plugin API to add your filter to it.
$_imgs = apply_filters('isc_images_in_posts', $_imgs, $post_id);
isc_images_in_posts_simple
This filter also runs on the images that are saved for a post, but it adds a meta field to the images containing the posts it is used in. These fields are used when showing the complete image list. If you don’t show the complete list of images on your post, you might not need this filter.
An element in the array that is filtered looks like this
1 => 'http://example.com/wp-content/uploads/2011/01/example-image.png'
The filter call looks like this. You can use the $post_id in case you need it. Use add_filter() like described on the Plugin API to add your filter to it.
$image_urls = apply_filters('isc_images_in_posts_simple', $image_urls, $post_id);