.load() on element to attach event handler in your behaviors should not be a problem. Using it directly to
window outside a behavior, for instance to wait for all images to be loaded, should be okay too.
As pointed by Clive in the comment, Drupal behaviors are to be used in replacement of
$.ready() will not be called and will not have a chance to process the added DOM elements. While the
attach() method of all behaviors is also called when this happen. With a parent of the added DOM elements as
Behaviors can also have a
detach() method which is called when DOM element are removed or before form serialization. This us, for instance, used to properly destroy WYSIWYG editors when their
textarea are removed from the DOM and to prepare the POSTed data hen their form are submitted.
Drupal.detachBehabiors(). Something that is done by Drupal core (including form handling and the Drupal AJAX Framework) and properly written contrib modules.
I'm not familiar with the
load event and its behavior with content added after the first time it is triggered. If it does not fire multiple times, re-registering the handler in a behavior
attach() method may be required to ensure newly added image are also processed.