Adding jquery to custom WP theme

So what do I need to do to get it working?

I’m not expert and just improvised the code which should resize image on window resize to be 80% of the shorter screen side maintaining ratio:

$(window).resize(function() {
	function imgResize()
	{

		if ($("#post_container img").width() > $("#post_container img").height()){

			$('#post_container img').css({ 'width': '80%', 'height': 'auto' });
			}
		else if ($("#post_container img").width() < $("#post_container img").height()){

			$('#post_container img').css({ 'width': 'auto', 'height': '80%' });
			}
		else {
			$('#post_container img').css({ 'width': '80%', 'height': 'auto' });
			}

	}

})

Is that even right?

I also have these in my functions.php:

function my_init_method() {
    if (!is_admin()) {
        wp_deregister_script( 'jquery' );
        wp_register_script( 'jquery', 'https://ajax.googleapis.com/ajax/libs/jquery/1.5/jquery.min.js');
        wp_enqueue_script( 'jquery' );
    }
}

add_action('init', 'my_init_method');

function add_my_script() {
wp_enqueue_script(
    're-size', // name your script so that you can attach other scripts and de-register, etc.
    get_template_directory_uri() . '/js/imageResize.js', // this is the location of your script file
    array('jquery') // this array lists the scripts upon which your script depends
);
}

add_action( 'wp_enqueue_scripts', 'add_my_script' );

// smart jquery inclusion
if (!is_admin()) add_action("wp_enqueue_scripts", "my_jquery_enqueue", 11);
function my_jquery_enqueue() {
   wp_deregister_script('jquery');
   wp_register_script('jquery', "http" . ($_SERVER['SERVER_PORT'] == 443 ? "s" : "") . "://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js", false, null);
   wp_enqueue_script('jquery');
}

Is there something extra or something missing?

And then I have this in my header.php in the head tag:

<?php wp_enqueue_script("jquery"); ?>

So whats wrong, too much or missing?