lib/Tumblr/API/Client.php
public function getBlogAvatar($blogName, $size = null)
    {
        $path = $this->blogPath($blogName, '/avatar');
        if ($size) {
            $path .= "/$size";
        }

        return $this->getRedirect($path, null, true);
    }
public function getBlogAvatar($blogName, $size = null)
    {
        $path = $this->blogPath($blogName, '/avatar');
        if ($size) {
            $path .= "/$size";
        }

        return $this->getRedirect($path, null, true);
    }
Get blog avatar URL

@param string $blogName the nae of the blog to look up
@param int    $size     the size to retrieve

@return string the avatar url