This photo is part of a photo set of a herd of feral horses in Namibia. The set provides an interesting look at daily wild horse behavior, from sparring to napping. Here a few horses keep watch while others rest. Follow the flickr link to enjoy more pictures of these horses.
This article, though it dates from 1999, has some interesting info about the horses. Though I am unaware of their origins, the feral horses of Namibia have become a tourist attraction, and their population is sometimes stricken by drought, as was the case in 1999, when a controversial effort was made to save them.
The feral horses were featured in a fictional film called "Running Free", by Jean-Jacques Arnaud (director of "Seven Years in Tibet" and "Name of the Rose"), which has contributed to their popularity with visitors. The film is a classic horse and boy story of a stranded and suffering steed and the stable boy who loves him, who flee their cruel master to face the freedom of the desert. I haven't seen it, but will write a review if I do.
Photo: moonlight*1 on flickr