A few years ago one of our resident wags commented, when he saw the image of our Lady veiled for Passiontide, "Ooh, she looks like our Lady of Afghanistan now!"
Veiling images for Passiontide is part of our liturgical history and tradition. Passiontide is what the two weeks before Easter Sunday is called. It seems that it is in fact an older season than Lent itself. It is divided into the week after Lent V, known as Passion Week, and the week after Palm Sunday, known as Holy Week.
In former days, today, the Fifth Sunday of Lent, used to be called "Passion Sunday" because it began the season of Passiontide. In fact, that was just shorthand for "Passion Sunday I", the following Sunday being "Passion Sunday II". But Passion Sunday II was also better known as "Palm Sunday", for obvious reasons. Historically, the much earlier usage of the name "Passion Sunday" belonged to Palm Sunday, not to Lent V. This is because on Palm Sunday, after the joyful Procession commemorating the Lord's triumphant entry to Jerusalem, the mood of the Liturgy shifts and the Mass becomes the Mass of the Passion, with the solemn reading of the Passion narrative as the Gospel. This shift was also marked in the old rite by the priest changing vestments, from red for the procession, to purple for the Mass (this no longer happens).
When the Liturgy and Liturgical Calendar were reformed after the Second Vatican Council, this more ancient usage of the name "Passion Sunday" was restored. Except, people knew what Palm Sunday was, and were not about to start calling it Passion Sunday! An attempt at compromise was used by some liturgists and parishes in calling it "Passion/Palm Sunday", which was inelegant in the extreme. What we now have is the much better description of it as Palm Sunday of the Lord's Passion - though we still tend to call it simply Palm Sunday!
The veiling of images probably has a simple origin, based on cultural customs, with a theological meaning later added. One such is that it comes from the former Gospel reading for Lent V (the old Passion Sunday), John 8:46-59. The last verse reads:
So they picked up stones to throw at him, but Jesus hid himself and went out of the temple.
This hiding of himself was represented by the veiling of images of Jesus, later extended to all images in the church.
There are other reasons given by some in an attempt to provide a more theological explanation. Some authors suggest that it is a sign of Christ's divinity being hidden at the time of his Passion. Or that we should make a concerted mental effort in contemplating the Lord's Passion at this time, and not have images to focus on. On Good Friday, one option for the Veneration of the Cross is for it to be uncovered in stages while the refrain is sung: This is the Wood of the Cross on which hung the Saviour of the World. Come, Let us worship! (At Newman House we use the other option, which is to process the Cross through the Church, so it is not ritually uncovered).
So that is why we now have "our Lady of Afghanistan" in our Chapel!