opencv motion tracker with identification

Currently, the following script works perfectly fine, but I now want to give each rectangular bound box an identifier.

while True:
    # grab the current frame and initialize the occupied/unoccupied
    (grabbed, frame) = camera.read()

    if not grabbed:
        break

    # resize the frame, convert it to grayscale, and blur it
    frame = imutils.resize(frame, width=500)
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    gray = cv2.GaussianBlur(gray, (21, 21), 0)

    # if the first frame is None, initialize it
    if firstFrame is None:
        firstFrame = gray
        continue

    # compute the absolute difference between the current frame and
    # first frame
    frameDelta = cv2.absdiff(firstFrame, gray)
    thresh = cv2.threshold(frameDelta, 25, 255, cv2.THRESH_BINARY)[1]

    # dilate the thresholded image to fill in holes, then find contours
    # on thresholded image
    thresh = cv2.dilate(thresh, None, iterations=2)
    (_, cnts, _) = cv2.findContours(thresh.copy(),   cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

    # loop over the contours
    for c in cnts:
        # if the contour is too small, ignore it

        if cv2.contourArea(c) < args["min_area"]:
            continue

        # compute the bounding box for the contour, draw it on the frame
        (x, y, w, h) = cv2.boundingRect(c)
        cv2.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 2)

For example, given the following image:

I want to be able to identify each of the four rectangular bounds as an object. (i.e. the leftmost is a bound box for the Queen of Diamonds card, and the rightmost is a bound box for the Ace of Hearts card)

Right now, I am stumped as to how I could possibly achieve this, and was wondering if anyone could give me inspiration.