Change default input() function behaviour. You may use this hook to perform addtional checks to user input.

<?php
function my_component_init(){
		ossn_add_hook('ossn', 'input', 'my_component_hook');
}
function my_component_hook($hook, $type, $return){
		//$return[input] Input contain the name of input
		//$return[noencode] To enacode or not
		//$return[default] Default data if empty input,
		//$return[strip] strip spaces (trim) default is true,
		//$return[data] Actual data
		return $return;
}
ossn_register_callback('ossn', 'init', 'my_component_init');

Example of this use case https://www.opensource-socialnetwork.org/component/view/3868/reduce-images-size