Sergey Biryukov

<?php
function show_user_name_in_avatar_alt_text($html, $params) {
    if ( $params['object'] == 'user' ) {
        $userdata = get_userdata($params['item_id']);
        $html = preg_replace('/alt=".*?"/', 'alt="' . $userdata->display_name . '" title="' . $userdata->display_name . '"', $html);
    }
    return $html;
}
add_filter('bp_core_fetch_avatar', 'show_user_name_in_avatar_alt_text', 10, 2);
?>