Image Element: SRCset & Alt Not Inserted?

The image element only auto-inserts an image’s SRCset and Alt attributes if an image in the media library is specified or “{featured_image}” is entered under Dynamic Data.

I wrote a PHP function named ft_img__tap() that retrieves a parent page’s featured image when a child page does not have a featured image specified. When I enter “{echo:ft_img__tap}” under Dynamic Data, the image appears, but the SRCset and Alt attributes are not automatically inserted.

My function returns an array:
[0] =>
[1] => 713
[2] => 845
[3] =>
[alt] => disney_star_wars

1 = width & 2 = height

In order for Bricks to automatically insert SRCset and Alt attributes, my function needs to return data in what kind of format?