这应该可以工作：

import numpy as np
import cv2
import Tkinter as tk
import Image, ImageTk

#Set up GUI
window = tk.Tk()  #Makes main window
window.wm_title("Digital Microscope")
window.config(background="#FFFFFF")

#Graphics window
imageFrame = tk.Frame(window, width=600, height=500)
imageFrame.grid(row=0, column=0, padx=10, pady=2)

#Capture video frames
lmain = tk.Label(imageFrame)
lmain.grid(row=0, column=0)
cap = cv2.VideoCapture(0)
def show_frame():
    _, frame = cap.read()
    frame = cv2.flip(frame, 1)
    cv2image = cv2.cvtColor(frame, cv2.COLOR_BGR2RGBA)
    img = Image.fromarray(cv2image)
    imgtk = ImageTk.PhotoImage(image=img)
    lmain.imgtk = imgtk
    lmain.configure(image=imgtk)
    lmain.after(10, show_frame) 


#Slider window (slider controls stage position)
sliderFrame = tk.Frame(window, width=600, height=100)
sliderFrame.grid(row = 600, column=0, padx=10, pady=2)

show_frame()  #Display 2
window.mainloop()  #Starts GUI

首先，您有行tk.Label(imageFrame, image=show_frame()).grid(row=0, column=0, padx=10, pady=2)，由于show_frame()不返回任何内容，因此将image设置为None。其次，你需要确保你的lmain.grid()，否则lmain不会显示。
如果你想有两个显示器，一个在另一个的上面，你可以这样做：

import numpy as np
import cv2
import Tkinter as tk
import Image, ImageTk

#Set up GUI
window = tk.Tk()  #Makes main window
window.wm_title("Digital Microscope")
window.config(background="#FFFFFF")

#Graphics window
imageFrame = tk.Frame(window, width=600, height=500)
imageFrame.grid(row=0, column=0, padx=10, pady=2)

#Capture video frames

cap = cv2.VideoCapture(0)

def show_frame():
    _, frame = cap.read()
    frame = cv2.flip(frame, 1)
    cv2image = cv2.cvtColor(frame, cv2.COLOR_BGR2RGBA)
    img = Image.fromarray(cv2image)
    imgtk = ImageTk.PhotoImage(image=img)
    display1.imgtk = imgtk #Shows frame for display 1
    display1.configure(image=imgtk)
    display2.imgtk = imgtk #Shows frame for display 2
    display2.configure(image=imgtk)
    window.after(10, show_frame) 

display1 = tk.Label(imageFrame)
display1.grid(row=1, column=0, padx=10, pady=2)  #Display 1
display2 = tk.Label(imageFrame)
display2.grid(row=0, column=0) #Display 2

#Slider window (slider controls stage position)
sliderFrame = tk.Frame(window, width=600, height=100)
sliderFrame.grid(row = 600, column=0, padx=10, pady=2)

show_frame() #Display
window.mainloop()  #Starts GUI

试试这个代码：

from PIL import Image, ImageTk
import Tkinter as tk
import argparse
import datetime
import cv2
import os

class Application:
    def __init__(self, output_path = "./"):
        """ Initialize application which uses OpenCV + Tkinter. It displays
            a video stream in a Tkinter window and stores current snapshot on disk """
        self.vs = cv2.VideoCapture(0) # capture video frames, 0 is your default video camera
        self.output_path = output_path  # store output path
        self.current_image = None  # current image from the camera

        self.root = tk.Tk()  # initialize root window
        self.root.title("PyImageSearch PhotoBooth")  # set window title
        # self.destructor function gets fired when the window is closed
        self.root.protocol('WM_DELETE_WINDOW', self.destructor)

        self.panel = tk.Label(self.root)  # initialize image panel
        self.panel.pack(padx=10, pady=10)

        # create a button, that when pressed, will take the current frame and save it to file
        btn = tk.Button(self.root, text="Snapshot!", command=self.take_snapshot)
        btn.pack(fill="both", expand=True, padx=10, pady=10)

        # start a self.video_loop that constantly pools the video sensor
        # for the most recently read frame
        self.video_loop()

    def video_loop(self):
        """ Get frame from the video stream and show it in Tkinter """
        ok, frame = self.vs.read()  # read frame from video stream
        if ok:  # frame captured without any errors
            cv2image = cv2.cvtColor(frame, cv2.COLOR_BGR2RGBA)  # convert colors from BGR to RGBA
            self.current_image = Image.fromarray(cv2image)  # convert image for PIL
            imgtk = ImageTk.PhotoImage(image=self.current_image)  # convert image for tkinter
            self.panel.imgtk = imgtk  # anchor imgtk so it does not be deleted by garbage-collector
            self.panel.config(image=imgtk)  # show the image
        self.root.after(30, self.video_loop)  # call the same function after 30 milliseconds

    def take_snapshot(self):
        """ Take snapshot and save it to the file """
        ts = datetime.datetime.now() # grab the current timestamp
        filename = "{}.jpg".format(ts.strftime("%Y-%m-%d_%H-%M-%S"))  # construct filename
        p = os.path.join(self.output_path, filename)  # construct output path
        self.current_image.save(p, "JPEG")  # save image as jpeg file
        print("[INFO] saved {}".format(filename))

    def destructor(self):
        """ Destroy the root object and release all resources """
        print("[INFO] closing...")
        self.root.destroy()
        self.vs.release()  # release web camera
        cv2.destroyAllWindows()  # it is not mandatory in this application

# construct the argument parse and parse the arguments
ap = argparse.ArgumentParser()
ap.add_argument("-o", "--output", default="./",
    help="path to output directory to store snapshots (default: current folder")
args = vars(ap.parse_args())

# start the app
print("[INFO] starting...")
pba = Application(args["output"])
pba.root.mainloop()