Get Alt and insert into my theme

Hi!

I’have a probleme, i’m new on wordpress and I don’t arrive to add the alt attribut and the other title and caption. I try many thinks like
$alt = get_post_meta($attachment->ID, '_wp_attachment_image_alt', true);
but nothing works for me, somebody can help me?

I have this code on my theme:

add_shortcode('flex_slider','wpts_flex_slider');
	$string = '';
	function wpts_flex_slider_item($atts, $content = null, $code)
	{
		extract(shortcode_atts( array(
			'src' => '',
			'caption' => '',
			'href' => '',
			'alt'  => '',
		), $atts));
		$hclose = '';
		if($href!= '')
		{
			$href = '<a href="'.$href.'">';
			$hclose = '</a>';
		}

		$html = '
		<li>
			'.$href.'<img src="'.$src.'" alt="'.$alt.'" />'.$hclose.'

		</li>';
		return $html;
	}