I update the latest nodebb, found the following issue:
The latest one is a transparent png, there is a line cross it..
@sharonyue You should be able to work around this using CSS class z-index - can you provide a URL where I can view ?
@phenomlab You can see it from here 
@sharonyue Try this
.topic .posts>[component=post] .avatar, .topic .posts>[component=post] .timeline-badge, .topic .timeline-event .avatar, .topic .timeline-event .timeline-badge {
background: #ffffff;
}
This will place a white background over the image matching this class - it'll only show for transparent images, and will probably solve the issue. However, you'll need to check other areas of the site and perhaps adjust the CSS to suit if necessary.
@phenomlab Thank you! It works like a charm!!
Do you think if nodebb needs to fix it as a bug? instead of CSS?
@sharonyue No, I don't think so. It's unusual for avatar images to have transparent backgrounds
