[@robkk Moderator 11 years, 1 month ago]

Add this custom CSS anywhere you can put custom css like your child themes style.css file or a custom css plugin.

#bbpress-forums p.bbp-topic-meta img.avatar, 
#bbpress-forums ul.bbp-reply-revision-log img.avatar, 
#bbpress-forums ul.bbp-topic-revision-log img.avatar, 
#bbpress-forums div.bbp-template-notice img.avatar, 
#bbpress-forums .widget_display_topics img.avatar, 
#bbpress-forums .widget_display_replies img.avatar {
    float: none;
    margin-bottom: 0;
    vertical-align: middle;
    border: 1px solid #ddd;
}

You can use this function (and add it where you can put php code snippets, like your child themes functions.php file or in a plugin like functionality) in this topic to increase those 14px avatars to say 24px.

Resizing Avatars