How do you browse and upload a photo from an iPhoto Library to a website using a browser like Safari, Chrome, Firefox, etc

How do you browse and upload a photo from an iPhoto Library to a website
using a browser like Safari, Chrome, Firefox, etc

I've at a site that wants me to upload a photo. I choose Browse... but
when I get to iPhoto Library, it's opaque. Is there some way to browse and
choose one?