Customized Blog Avatars

I am following the Codex instructions here (at bottom of page) without much success.

The new selector under Settings > Discussion shows up, but the image is not being displayed. Here is the HTML that is being outputted for the new selector:

<label>
<input type="radio" name="avatar_default" id="avatar_https://localhost/testacy/wp-content/themes/twentyfifteenimages/awc-avatar.png" value="https://localhost/testacy/wp-content/themes/twentyfifteenimages/awc-avatar.png" checked="checked">

<img alt="" src="https://1.gravatar.com/avatar/d6055c675824b5b2927c761b66542f19?s=32&d=http%3A%2F%2Flocalhost%2Ftestacy%2Fwp-content%2Fthemes%2Ftwentyfifteenimages%2Fawc-avatar.png&r=g&forcedefault=1" srcset="https://1.gravatar.com/avatar/d6055c675824b5b2927c761b66542f19?s=64&d=http%3A%2F%2Flocalhost%2Ftestacy%2Fwp-content%2Fthemes%2Ftwentyfifteenimages%2Fawc-avatar.png&r=g&forcedefault=1 2x" class="avatar avatar-32 photo" height="32" width="32"> Custom Avatar
</label

Notice that the image link above is actually comprised of two URLs: one to Gravatar, and the other to a local directory supposedly containing the image. This raises two questions:

• Where is the file responsible for inserting this rogue Gravatar link, so that I may override?
• What is ‘twentyfifteenimages’ referring to? I am confused as to where I should actually be placing my image. It should go in my child theme, for obvious reasons…but unsure at this point.