Custom gravitar not showing up in dashboard or on comments

I used the following code from the codex to add a new default gravitar to a site, but something’s amiss.

Here’s the code from the codex…

add_filter( 'avatar_defaults', 'new_default_avatar' );

function new_default_avatar ( $avatar_defaults ) {
		//Set the URL where the image file for your avatar is located
		$new_avatar_url = get_bloginfo( 'template_directory' ) . '/images/new_default_avatar.png';
		//Set the text that will appear to the right of your avatar in Settings>>Discussion
		$avatar_defaults[$new_avatar_url] = 'Your New Default Avatar';
		return $avatar_defaults;
}

I put my new avatar in the images folder just like the code above describes and I’ve rechecked my file name a few times. My code editor verifies the image in my source file so I know it’s a proper file and it’s there.

Any ideas why my gravitar isn’t showing. I get a blank space. The choice for my gravitar does show up in the dashboard in Settings > Discussion, but with no icon, either. I have verified that the image IS in the images folder via FTP.

The only other clue is that when I click on the image, I do get a white screen with this note: “We cannot complete this request, remote data was invalid”. I did a search on that one, and there’s a lot of info about Jetpack and Photon, but I’m using neither on my site.

So, I’m stumped.