Simple one, use Gravatar instead of default image for your users if they haven't added a profile pic.
Thank you for the idea. Given the low volume of support for this idea, we do not have plans to make updates in this area at this time. It is currently possible to add avatars directly in personal settings. We hope that helps!
related idea
APP-I-6440
users shouldn't have to make a Gravatar account just to add a photo, though.