Changing the Default Avatar in WordPress

This post by Nikhil Misai cleared up some confusion I had yesterday. I had added a filter to override the avatar default with a local file in my template’s images directory, but every how-to I read neglected to mention the final step of setting the default avatar in the the Settings > Discussion settings. I had (incorrectly) assumed that the filter would override any avatar setting when rendering the final output, but it appears that the filter merely makes a new default available in the settings.