This solution enables you to add your own custom alt text to each featured image on single posts in Genesis.
You can add the alt text to each featured image when uploading, however you would need to remove the image and add it back if you wanted to add alt text after the image has already been added.
Video Demo
If no alt text is added manually, the title is added as the alt text by default.
The full code enables you to add the featured image on single posts with your own custom alt text.
This code provides a flexible solution supported for logged in members: