I'm calling media-upload.php via a custom icon click inside the content editor and I would like to add a custom meta value for all images that are uploaded when the media-upload.php is called from my custom function.
For example, for each of the images that are uploaded, I want to insert a value into wp_postmeta of _customAttachment = 1 like so:
update_post_meta($post['ID'], '_customAttachment', true);
I know how I can pass the current post-id to the media-upload.php (via querystring parameters), but I have no idea how to attach my update_post_meta filter to the save/upload trigger in media-upload.php
Is there a filter for this?