Disclaimer- I do not own Harry Potter. If I did I wouldnt have killed so many characters in Deathly Hallows...
Prologue
The seemingly most mundane of objects are often those who hold the most mystifying qualities. They are also, usually, owned by both Muggles and Wizards, thus not attracting adverse attention to themselves- such as Two Way Mirrors that look and act like a normal mirror, yet allow two Wizards to communicate over long distances, like a mobile phone... without the phone bills...
It is through this logic that Fakirs of Arabia during the 1st Century AD, took the Muggle idea of painting portraits of the dead to be placed with the body on burial as an eternal record of the deceased's likeness, and devised the Wizarding Portrait.
Like the Muggle Fayum mummy portraits, the Wizarding Portraits depicted a deceased's likeness. However, through carefull spell casting, the Fakirs were able to divert the spirit of the Witch or Wizard from passing directally to the spirit world at death into a specific canvas -or set of canvases-, acting as a medium between the Land of the Living and the Spirit world.
Thus, the soul of the deceased free to travel between the Land of the Living and the Spirit world, though many choose to remain in their portrait which is usually hung in the family home or in an institution.
The spells to create the Wizarding Portrait, however, gave rise to the creation of the Horcrux by accident in the 5th Century when a portrait maker -who had avenged his brothers murderer- mispronounced the incantation Spiritus Averto (from the Latin "Soul Divert") as Spiritus Averti (which roughly translates as "Soul Rout"), thus embedding the piece of his soul which had been torn into the canvas of the portrait he was making.
The creation of the Horcrux was not known until the Horcurx Portrait was destroyed in a fire some 150 years after its manufacture. The portrait maker, who was then in his 175th year, had always had a fondness for the portrait that he "couldn't quite explain", and when the occupant of the portraits' family had all died, he had taken the portrait home with him.
He had died but a week after the Horcrux being destroyed, after being through by a sword during a street show.
He had completed the feat many a time before after discovering years earlier that he could not die after being –what would normally be fatally- impaled with a spear.
The connection between the Horcrux and immortality was soon recognised by vain and Dark wizards alike, and thus the practice was prohibited by the governing bodies of the time.
This did not perturb those from attempting to create Horcruxes, though, and was only outlawed by the Dark wizards after a spate of horrific deaths due to soul fragility.
To date, the only wizard to create a successful Horcrux is Tom Riddle, also known as Lord Voldemort, who split his soul 7 times (not including the piece remaining in his being).
Unlike the Horcrux, the Spiritus Averto charm can be used on a soul numerous times without affecting its integrity. In fact, most wizards' souls are linked to a number of portraits, the first of which is created, usually, at birth.
Around the age when Muggle children are baptised –or other such religious rite is completed-, Wizarding children have their soul connected to a canvas in a linking ceremony known as Conserui (from the Latin "link").
The Conserui is also performed at weddings and various inductions.
This linking of one soul to many canvases allows the soul to travel between the various portraits which may be hung in various establishments in different parts of the country or, in some cases, in a different country entirely.
R&R because it makes me feel special... and if there are any grammatical errors that I have missed, please say so.
... writing Land of the Living and Spirit world made me think of His Dark Materials...