Taxonomy image in WIDGET

$cats = get_categories();
foreach ( $cats as $c ) {
    $url = get_category_link( $c->term_id );
    $img = $taxonomy_images_plugin->get_image_html( 'detail', $c->term_taxonomy_id );
    if( !empty( $img ) )
        print '<a href="' . $url . '">' . $img . '</a>';
}

hi, if a place this code(from plugin page) inside a sidebar or widget, it doesnt works, if there is anybody how have made a plugin or widget help me i’ll preciated your support,… this is the error:

Fatal error: Call to a member function get_image_html() on a non-object in /home/codigo12..../.././..

I tried to place “global $wpdb;”, but it doesn work!..