Which hook is invoked when pressing the remove button with widget image? In a content type named "R" there is a image field say "I". When a node with R->I is filled with a image file then standard you can remove this by pressing the remove button.  The standard images widget is used in drupal 7.

When I press this remove button something is executed as I get a message just 2 cm above the field "I" which is displaying the following message:


  content_type_name, content_type_title has been updated.


How do I find out which hook is invoked?
This message is coming from node_form_submit.
That function subsequently calls node_save which in turn calls the following hooks:

// Let modules modify the node before it is saved to the database.
module_invoke_all('node_presave', $node);
module_invoke_all('entity_presave', $node, 'node');
...
module_invoke_all('node_' . $op, $node);
module_invoke_all('entity_' . $op, $node, 'node');


where $op is one of 'update' or 'insert'.