Adding alt tag to Author images

Hi there!

I'm trying to add alt tags to the author images on our site. I've been able to do so in a custom author box, but on the author archive pages I'm not sure how I do this.

This is the code I have for the post author box:

So as you can see I use the author name as the alt tag.

When I inspect the author archive images, this is the result:

How can I add a similar alt tag in the archive page?

Thanks!