This is from the Wikipedia article on The Day of the Dead:
The Day of the Dead (Día de los Muertos in Spanish) is a holiday celebrated mainly in Mexico and by people of Mexican heritage (and others) living in the United States and Canada. The holiday focuses on gatherings of family and friends to pray for and remember friends and relatives who have died. The celebration occurs on the 1st and 2nd of November, in connection with the Catholic holy days of All Saints’ Day and All Souls’ Day which take place on those days. Traditions include building private altars honoring the deceased, using sugar skulls, marigolds, and the favorite foods and beverages of the departed, and visiting graves with these as gifts.
Scholars trace the origins of the modern holiday to indigenous observances dating back thousands of years, and to an Aztec festival dedicated to a goddess called Mictecacihuatl (known in English as "The Lady of the Dead").
There’s lots more interesting content, but this part explains the striking photo:
José Guadalupe Posada created a famous print of a figure that he called "La Calavera de la Catrina" ("calavera of the female dandy"), as a parody of a Mexican upper class female. Posada’s striking image of a costumed female with a skeleton face has become associated with the Day of the Dead, and Catrina figures often are a prominent part of modern Day of the Dead observances. [continue]