1.Log in to your dashboard--> layout- -> Edit HTML.
2.Click on "Expand Widget Templates"
3.Scroll down to where you see this:
<span class='post-author vcard'>
<b:if cond='data:top.showAuthor'>
<data:top.authorLabel/>
<span class='fn'><data:post.author/></span>
</b:if>
</span>
4.Replace <data:post.author/> with below code:
<a href="URL OF YOUR BLOG"><img src="URL OF YOUR PICTURE" /></a>
5.Click on "Save Templates" and refresh your site.
Note : Remember to give your real information to URL OF YOUR BLOG and URL OF YOUR PICTURE.
File Under : change template, html, image
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