it is the avatar image that does not have an alt tag <img alt='' src='http://0.gravatar.com/avatar/06911c6c697d05869d348395d9c39de9?s=32&d=http%3A%2F%2F0.gravatar.com%2Favatar%2Fad516503a11cd5ca435acc9bb6523536%3Fs%3D32&r=G' class='avatar avatar-32 photo' height='32' width='32' /> thanks.
Sorry Guys.. it is the images used for the avatars that do not have an Alt tag. <img alt='' src='http://0.gravatar.com/avatar/06911c6c697d05869d348395d9c39de9?s=32&d=http%3A%2F%2F0.gravatar.com%2Favatar%2Fad516503a11cd5ca435acc9bb6523536%3Fs%3D32&r=G' class='avatar avatar-32 photo' height='32' width='32' />
Hello, Gravatar image is fetched through WordPress default comment function. It is not possible to make any changes in it. You can use any alt tag plugin from WordPress.org.