Question

When I move an image around my PyGame screen, if it happens to pass over another image, those onderneath get hidden and cannot be seen again. Why might this be?

My code is:

def main():
    screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))

    background = pygame.image.load('Background.png').convert()
    screen.blit(background, (0, 0))  # draw the background screen

    human1 = pygame.image.load('Human1.gif').convert()
    human1_position = pygame.Rect(10, BOTTOM_FLOOR, CHARACTER_WIDTH, CHARACTER_HEIGHT)
    screen.blit(human1, human1_position)  # draw the first human

    human2 = pygame.image.load('Human2.gif').convert()
    human2_position = pygame.Rect(100, BOTTOM_FLOOR, CHARACTER_WIDTH, CHARACTER_HEIGHT)
    screen.blit(human2, human2_position)  # draw the second human

    human3 = pygame.image.load('Human3.gif').convert()
    human3_position = pygame.Rect(190, BOTTOM_FLOOR, CHARACTER_WIDTH, CHARACTER_HEIGHT)
    screen.blit(human3, human3_position)  # draw the third human

    pygame.display.update()  # display all graphical elements

    move = STOP  # Variable to track what the current move is. Initially, stopped
    move_character = 1  # Variable to track which character is being moved

    while True:
        #
        # See what the user did...
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                sys.exit()
            elif event.type == pygame.KEYDOWN:

                # Check if there is a move currently happening. The program
                # will only do something if the previous move is stopped
                if move == STOP:
                    # Check which key was pressed...
                    if event.key == pygame.K_1:
                        # if key pressed is the '1' key, move first human (and check if moving from bottom to top or other way)
                        move_character = 1  # the first character is to be moved
                        if human1_position.top < 300:
                            # If the 'top' of the human's position is less 
                            # than 300 then it means the human is currenlty
                            # on the top half of the screen, and so
                            # the next move will be to move it downards
                            move = DOWN
                        else:
                            move = UP

                    # Check which key was pressed...
                    if event.key == pygame.K_2:
                        # if key pressed is the '2' key, move second human (and check if moving from bottom to top or other way)
                        move_character = 2 # the first character is to be moved
                        if human2_position.top < 300:
                            # If the 'top' of the human's position is less 
                            # than 300 then it means the human is currenlty
                            # on the top half of the screen, and so
                            # the next move will be to move it downards
                            move = DOWN
                        else:
                            move = UP

            screen.blit(background, human1_position, human1_position) # erase old position of first human
            if (move == UP):
                #they want to move up, so first check the lift is down with them.
                if (liftLoc == "down"):
                    #they are both down, they can be moved into the lift
                    if (human1_position.left <= 245):
                        human1_position = human1_position.move(2, 0)  # move first human
                        pygame.display.update()
                    else:
                        move = STOP
                else:
                    print "Wrong floor!"

Answer 1

So the problem you are having, is that you are only rendering/blitting the images you move over when you start, so they get “unrendered” or rendered over.
To get rid of this problem, like all other real time rendering engines, you should render everything you want someone to see, every frame you want something to happen.

I shall not give you the code correction, but just moving the screen.blit of every image into your while loop. Their position will obviously affect the rendering order.