Facebook is introducing a new feature to allow blind and visually impaired people to "see" photos.

People using the social media site on an iOS device can now hear a list of items shown in the photo, such as people smiling or trees.

Previously, the screen reader feature would only tell the blind and visually impaired that an image had been uploaded, but not what was in it.

Facebook's Shaomei Wu, Hermes Pique, and Jeffrey Wieland said in a blog post that blind people "often feel frustrated and even excluded or isolated" by not being able to take part in conversations about photos.

"While this technology is still nascent, tapping its current capabilities to describe photos is a huge step toward providing our visually impaired community with the same benefits and enjoyment that everyone else gets from photos on Facebook," they said in the online post.

The feature, called automatic alternative text, has been introduced on iOS devices in English for people in the UK, USA, Canada, Australia and New Zealand.

Facebook said it expects to widen its availability in the near future.

The descriptions will initially be restricted to a vocabulary of 100 words, but Facebook hopes to refine the technology so it provides more precise descriptions and even answers questions that a user might pose about a picture.