I’ve heard it said that this is not a “painting” it’s and “icon”.
The Akathist calls it that here:
Thy humble servant went with joy and great anticipation to the palace of the bishop with the roses Thou didst give him as evidence of Thy appearance. Believing the flowers to be the final signal to all affirming Thy coming on earth, Juan unfurled his tilma. Upon
seeing the greater miracle of Thy image not made by human hands, all cried: Alleluia!
The bishop joined with everyone in kneeling prayerfully before Thy miraculous Icon, bowing to God’s revelation of His salvation of the Americas through His Most Holy Mother. Spellbound in wonder and amazement at Thy great love for those for whom Thy Son died for on the Precious and Life-giving Cross, they all sang:
Rejoice, Icon revealing Thy Son and Lord Jesus Christ!
Rejoice, Image reflecting His Heavenly Glory!
Rejoice, Sign from Heaven, bringing us the Abundant Life!
Rejoice, our Mantle of Protection!
Rejoice, covering us with an outpouring of Grace!
Rejoice, Who appears to us when we know neither the day nor the hour!
Rejoice, for Thou didst call us to the Kingdom of God suddenly!
Rejoice, Who imprints the image of Thy Son on those who honour Thee!
Rejoice, Robe of salvation!
Rejoice, Armour of Christ!
Rejoice, Witness to the Divine Incarnation!
Rejoice, Holy Garment without seam!
Rejoice, O Lady from Heaven, Virgin-Mother clothed with the Sun!
Later on, the tilma is compared to the Mantle of Divine Protection of the Most Holy Theotokos (Agia Skepi) which she spread over the City to protect it from its enemies.
Hillary recently asked who the artist was. I think the Bishop responded “God”.