Place the black olives, pimento-stuffed green olives, artichoke hearts, onion, celery, garlic, and capers in the bowl of a food processor. Pulse until the ingredients are uniform in size, and no larger than a popcorn kernel. Stir in the Italian dressing. Add equal amounts of green and black olive brine as needed for a moist consistency. Season with salt and black pepper. Chill in the refrigerator for at least 12 hours before serving.