Sorry for my late reply. I appreciate your quick action! I needed some time to look deeper into the problem and learn to use “grep”. We are using the theme “Newspaper”: https://themeforest.net/item/newspaper/5489609
I looked into the files newspapers offers and here is what I found:
./Newspaper/functions.php: $author_avatar = get_avatar( bbp_get_topic_author_id( $topic_id ), $size );
./Newspaper/functions.php: $author_avatar = get_avatar( get_post_meta( $topic_id, '_bbp_anonymous_email', true ), $size );
./Newspaper/includes/shortcodes/td_block_authors.php: $buffy .= '<a href="' . get_author_posts_url($td_author->ID) . '">' . get_avatar($td_author->user_email, '70') . '</a>';
./Newspaper/includes/shortcodes/td_block_author.php: $buffy .= '<a href="#">' . get_avatar('', '196') . '</a>';
./Newspaper/includes/shortcodes/td_block_author.php: $buffy .= '<a href="' . get_author_posts_url($td_author->ID) . '">' . get_avatar($td_author->user_email, '196') . '</a>';
./Newspaper/includes/wp_booster/td_module_single_base.php: $buffy .= get_avatar(get_the_author_meta('email', $author_id), '96');
./Newspaper/includes/wp_booster/comments.php: //echo get_avatar($td_comment_auth_email, 50, get_template_directory_uri() . "/images/avatar.jpg");
./Newspaper/includes/wp_booster/comments.php: echo get_avatar($td_comment_auth_email, 50);
./Newspaper/mobile/comments.php: //echo get_avatar($td_comment_auth_email, 50, get_template_directory_uri() . "/images/avatar.jpg");
./Newspaper/mobile/comments.php: echo get_avatar($td_comment_auth_email, 50);
./Newspaper/mobile/parts/logged.php: <div class="td-menu-avatar"><div class="td-avatar-container">' . get_avatar($current_user->ID, 80) . '</div></div>
./Newspaper/mobile/parts/login.php: <div class="td-menu-avatar"><div class="td-avatar-container">' . get_avatar($current_user->ID, 80) . '</div></div>
./Newspaper/mobile/author.php: <?php echo get_avatar($part_cur_auth_obj->user_email, '96'); ?>
./Newspaper/parts/logged.php: <div class="td-menu-avatar"><div class="td-avatar-container">' . get_avatar($current_user->ID, 80) . '</div></div>
./Newspaper/parts/login.php: <div class="td-menu-avatar"><div class="td-avatar-container">' . get_avatar($current_user->ID, 80) . '</div></div>
./Newspaper/parts/page-author-box.php: <?php echo get_avatar($part_cur_auth_obj->user_email, '96'); ?>
./Newspaper/parts/header/top-menu.php: get_avatar($current_user->ID, 20) . '<a href="' . get_author_posts_url($current_user->ID) . '" class="td_user_logd_in">' . $current_user->display_name . '</a>' .