In this podcast from his series looking at some of what's new and notable in iOS 15, Thomas Domville Shows us the improved image description capabilities for VoiceOver users.
Here’s how Apple describes this feature:
Building on recent updates that brought Image Descriptions to VoiceOver, users can now explore even more details about the people, text, table data, and other objects within images. Users can navigate a photo of a receipt like a table: by row and column, complete with table headers. VoiceOver can also describe a person’s position along with other objects within images — so people can relive memories in detail, and with Markup, users can add their own image descriptions to personalize family photos.