How to fix missing alt tag for avatars in blogger

I have the problem that all SEO-tools are showing a missing alt-tag for the avatar images in blogger. How can I fix this? The following codes I have found:

if (entry.author && entry.author.constructor === Array) {
          var auth = entry.author[0];
          if (auth) {
            comment.author = {
              name: (auth.name ? auth.name.$t : undefined),
              profileUrl: (auth.uri ? auth.uri.$t : undefined),
              avatarUrl: (auth.gd$image ? auth.gd$image.src : undefined)
            };

<b:if cond='data:comment.favicon'>
            <img expr:src='data:comment.favicon' height='16px' alt='Avatar' style='margin-bottom:-2px;' width='16px'/>
          </b:if>
          <a expr:name='data:comment.anchorName'/>
          <b:if cond='data:blog.enabledCommentProfileImages'>
            <data:comment.authorAvatarImage/>

Has someone an idea? alt='Avatar' doesn't work, also expr:alt='Avatar' doesn' work...

Thank you very much!