Sidebar custom output

Question

I have a call to register_sidebar:

<?php
if ( function_exists('register_sidebar') )
    register_sidebar(
        array(
        'before_widget' => '<div id="%1$s" class="widget entry %2$s">',
        'after_widget'  => '</div>',
        'before_title'  => '<h2 class="widgettitle">',
        'after_title'   => '</h2>'
        )
    );
?>

But I want the output to be:

<h2><img src="http://imagegenerator?text={title}" alt="{title}" /></h2>

Where the {title} is replaced with the current widget title, I cant seem to get the widget title. And to be honest I have no idea where those %1$ and %2$ variables have come from or are populated from.,

Is there a way to do this?