In my Yahoo profile and everywhere else, my profile picture is a male silhouette. How can I put a picture of me there?

You can't. Yahoo has disabled avatars and editing of nicknames for now. They are making changes to profiles.

Unfotunately you can't. Yahoo are making 'behind the scenes' changes to Profiles. Whilst they do that, they have disabled the ability to edit nicknames and edit/add profile photos.

We may be able to change them at some time in the future, but we don't know when as Yahoo haven't given a date.

You can't for now. Yahoo is in process of changing the profile page, getting rid of it,and they decided to put nickname posting and picture posting on hold for now. Not sure when it will be allowed again, if ever.