Comments are an important part of a magazine project that I'm work on, even being featured extensively on the front-page itself. For this reason, commenters are not only required to be logged in but must also have a recognizable avatar.
Although it would be the easiest route, we decided to make social logins secondary at most (as a shortcut available only after account creation), so we're left with basically two options - ask users to upload a profile picture in the registration form or use the gravatar functionality embedded in wordpress and prompt them to make sure they have a profile pic associated with their email @gravatar.
Each with its own caveats:
The advantage of the gravatar route is that if there's one already in place no further steps need be taken. On the flip side, those who don't have one would have to go to a third party unknown site to complete the formalities. This issue can be alleviated by letting the registration finish and then programmatically upgrade the rights of the user as soon as the gravatar becomes available. However, it's still a hurdle.
The uploading route is more straightforward at first, with the cost of having everybody, gravatar user or not, upload a profile picture. Still not too rosy. First, there should be an opportunity to change the image later, with costs in terms of programming and space. But if the user later deletes the picture or changes it to something undesirable, we are given a tough choice - either leave it be (not nice) or demote them and hide their comments as well (not cool). Sure, there's this possibility with gravatar as well, but I think it's much less likely hence acceptable.
If the option to update the picture is left out, the sign-up process would wrap up in one step, with some people giving up on the picture upload field (maybe they're on mobile and don't have one handy) and not being able to add it later in order to gain the right to comment.
Based on target audience, I expect between 20 to 25% of new users to already have some gravatar in place.
So the question is what would be the most efficient route to make sure that only people who have a profile picture get to comment while maximizing their numbers.