An Icon is a depiction ,(painting, carving, etching..), of a holy figure or item in the Eastern Orthodox Christian faith, (saint,archangel,guardian angel,holy person, or cross..).
One thing most people don't realize, is that these blessed paintings/carvings/etchings/ depictions are the saint, archangel, or holy person looking out at us, blessing us.
So when those in the mixed media art field, take an icon and 'defile' it, by say, cutting out the face, and putting in say a scull face, or something, it is considered to be sacrilegious.
Now, if they don't care, that is their choice of course.
But, there are those who, knowing this, would not want to use such a picture in their artwork. I have seen the former, whereby the saint's picture was defiled. And I have seen beautiful artwork, reveling in the beauty of the depiction- creating either a stage/scene with the icon and embellishing, or just painting one in a respectful manner.
Another tidbit. The icon painters turned into the Palekh/Mystyora/Kholoui/Fedoskino painters ,(different types of Russian lacquered boxes and items which are very popular ).
These are just very brief, simplified bits of info for those who may be interested.:)