Replace the Default Anonymous Avatar on Blogger Comments
Step 1. Go to Dashboard - Template - click on the Edit HTML button
...click anywhere inside the code area and open the template search box by pressing the CTRL + F keys
Step 2. Type or paste this code in the search box, then hit Enter to find it:
</body>Step 3. Just above the </body> tag, add the following code:
<script src='http://code.jquery.com/jquery-latest.js'/>Step 4. Save the changes by clicking on the Save Template button
<script>
$("img[src='http://img1.blogblog.com/img/anon36.png']")
.attr('src', 'https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiIajCy5FvgC6hdll-zlM-aL2i9jTdgem1eybLYj-HDB7kCmDzLCzIJ6ntwp6ikRdL6zNdL0ZmC_bAzVbwkP0O0CnSAwOLvqy-2knn_BOq-PzRiqcBlVro7dcLgImTIfTE34_3ofVmze4k/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', 'https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjIudllm4gNe-bZdJ_z59AXiKMbw-0hnC98EekF4a4YqnoWVANDkqZeELH3PaP3Xy2n7us3Vm6HZ7Ll2mg07PWq6wB-jwiu7zh2LZc8OUJOwUXJD0Pqt8B7gFPyWRpBn7OXMhscvaubzvE/s1600/blogger-user.png')
.ssyby('blank')
</script>
Changing the default avatar
For Anonymous users: Replace the code in red with your image addressFor Blogger users: Replace the URL in blue with your own.
You can choose an avatar from here and then copy the url of it:

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiIajCy5FvgC6hdll-zlM-aL2i9jTdgem1eybLYj-HDB7kCmDzLCzIJ6ntwp6ikRdL6zNdL0ZmC_bAzVbwkP0O0CnSAwOLvqy-2knn_BOq-PzRiqcBlVro7dcLgImTIfTE34_3ofVmze4k/s200/default_avatar.gif

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXbXpj-QDa0U3ietCD8zmZqH57s4s9y25iAJBwA1R61ePhZccV03k3pL_UgmBa9OowEgA5t8HDE1CFyf39l1pgKoRwrcIUyNQw2I_e8-Rj5dwvdQDh1EHarR-4k7HlEMlhL9Pe3rwyDvY/s1600/facebook.gif

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgXiqR5ij9naJtfemQ_KQDG1b3B7BRbQv4QJbWL1dTW7WZXpp5YHFYtHU9U1r5fxociria-8LxOmU9cjhVo6ihm0UOOao82DhYYk042eO5cMU7HYdq9D7e3_xroPZRq2JWY4h55uVcZ3uQ/s1600/anonymous3.png

https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjvyFlXpjI_V4B4w6wn7Alsyyd7Pj5bDsL56vQRAGFh2qs5yO9BdQL1WgCP42Vo0aUheauTuPJkkqZAWftEZ4Y82zxsPLNmtf-4zkdYUQP0upKz-NgFDPN9IX6gDJVPGgwwI5xDipRfRv-e/s1600/blogger-user.png
That's it! If you found this trick useful, please consider sharing it.