Question

I’m trying to get first frame and keep it unchanged but it changes after every assignment to the other variable ( currImage = cv.QueryFrame(capture) ). What am I doing wrong?

#!/usr/bin/env python 
# -*- coding: utf-8 -*- 

import cv

cv.NamedWindow("w1", cv.CV_WINDOW_AUTOSIZE)

#SET CAMERA INDEX BELOW
camera_index = -1 

capture = cv.CaptureFromCAM(camera_index)
isRunning = True
firstImage = cv.QueryFrame(capture)

def repeat():
  global capture #declare as globals since we are assigning to them now
  global camera_index
  global isRunning
  global firstImage
  c = cv.WaitKey(100) % 0x100
  currImage = cv.QueryFrame(capture) 
  cv.ShowImage("w1",firstImage)

  if(c==27):
    isRunning = False

while isRunning:
    repeat()

Answer 1

Let me quote you two passages from the opencv wiki, namely this page: http://opencv.willowgarage.com/documentation/python/reading_and_writing_images_and_video.html

cvQueryFrame:
The function cvQueryFrame [...] is just a combination of GrabFrame and RetrieveFrame.

RetrieveFrame:
The function cvRetrieveFrame returns the pointer to the image grabbed.

What you are doing in your code not copying the object, you merely create another object pointing at the corresponding memory. Subsequent calls to the cvQueryFrame just modify the object, Therefor you have to copy it.
Try doing this:

import copy 
import cv

cv.NamedWindow("w1", cv.CV_WINDOW_AUTOSIZE)

#SET CAMERA INDEX BELOW
camera_index = -1 

capture = cv.CaptureFromCAM(camera_index)
isRunning = True
firstImage = copy.deepcopy(cv.QueryFrame(capture))

def repeat():
  global capture #declare as globals since we are assigning to them now
  global camera_index
  global isRunning
  global firstImage
  c = cv.WaitKey(100) % 0x100
  currImage = cv.QueryFrame(capture) 
  cv.ShowImage("w1",firstImage)

  if(c==27):
    isRunning = False

while isRunning:
    repeat()