Alt-text is to describe non-decorative images that add meaning. The parent commenter is correct on how you would implement accessible alt-text here.

In the top, your avatar is meant to to represent a link to your profile. That needs an alt attribute. The alt attribute should be the current user's name, "Your Profile", or something similar. When signed out, something like "Sign In" might work better.

In the featured projects, the avatar that's there is decorative. The litmus test for decorative images is that if the image wasn't there, would you be able to easily figure out what to do? The image is purely decorative, as the creator's name is adjacent to it. There you would add an empty alt tag, like `alt=""` (not the same as no alt text), as screen-readers know to ignore that image then.

I highly recommend this page by WebAIM on it: https://webaim.org/techniques/alttext/