Anonymous user do not want to show their name and other detail.before publishing comment blogger may ask for security check.
But when if some one comment using google account then image on google plus profile will be shown and if that user have blogger account then blogger icon appear in picture.
How to remove/change default avatar in blogger comment
First you have to login to your accountnow go to template and edit HTMLpress CTRL+F inside code area then a search box appearSearch for </body>
Style 1
paste the given code before </body>
<script src="http://code.jquery.com/jquery-latest.js"><script>$("img[src='http://img1.blogblog.com/img/anon36.png']") .attr('src', 'http://1.bp.blogspot.com/-Zphr2YJH_6w/T6ZZE4YeNBI/AAAAAAAACF0/Tyuj8hkOpdc/s1600/default_avatar.gif') .ssyby('blank') </script><script src="http://code.jquery.com/jquery-latest.js"><script>$("img[src='http://img2.blogblog.com/img/b36-rounded.png']") .attr('src', ' http://4.bp.blogspot.com/-i-AATMTeTn8/Uc5IqkzZjUI/AAAAAAAAA1c/6H76qiQqQdg/s256/blogger-icon.png') .ssyby('blank') </script>Style 2
for style 2 add given code before </body>
<script src="http://code.jquery.com/jquery-latest.js"><script>$("img[src='http://img1.blogblog.com/img/anon36.png']") .attr('src', 'http://1.bp.blogspot.com/-Zphr2YJH_6w/T6ZZE4YeNBI/AAAAAAAACF0/Tyuj8hkOpdc/s1600/default_avatar.gif') .ssyby('blank') </script><script src="http://code.jquery.com/jquery-latest.js"><script>$("img[src='http://img2.blogblog.com/img/b36-rounded.png']") .attr('src', ' http://4.bp.blogspot.com/-iJwnCYnG0xE/Uc5INso1x3I/AAAAAAAAA1U/LbI5zJdlfxs/s268/anonymous3.png ') .ssyby('blank') </script>
save your template and keep enjoying.