Q:

Why photoimages don't exist?

I will show a reduced portion of the code that gives me a problem.
_tkinter.TclError: image "pyimageN" doesn't exist - where N stays for 1, 2, 3, etc...
There is a first class that shows a menu using an image in the background.
class MenuWindow():    #in this class we show the main part of the program
    def __init__(self):
        self.Menu=Tk()
        self.MCanvas=Canvas(self.Menu)
        self.MCanvas.bind("<ButtonPress-1>",self.MenuClick)

        #unuseful lines that configure the window and the canvas#

        self.Background=PhotoImage(height=600,width=700)#a simple tkinter.PhotoImage object

        #other unuseful lines that draw the photoimage ( without reading any file, with the method put())#

        self.MCanvas.create_image((x,y),image=self.Background,state="normal")

        #unuseful lines that continue the drawing of the canvas#

And a second class that shows another window, using another image in the background. This class is launched by the first class via click binding of the function self.MenuClick.
class EditorWindow():    #in this class we show the main part of the program
    def __init__(self):
        self.Eenu=Tk()
        self.ECanvas=Canvas(self.Eenu)

        #unuseful lines that configure the window and the canvas#

        self.Background=PhotoImage(height=600,width=700)

        #other unuseful lines that draw the photoimage ( without reading any file , with the method put() )#

        self.ECanvas.create_image((x,y),image=self.Background,state="normal")#in this line i get the error

        #unuseful lines that continue the drawing of the canvas#

The complere traceback is the following:
Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.1/lib/python3.1/tkinter/__init__.py", line 1399, in __call__
    return self.func(*args)
  File "/Users/albertoperrella/Desktop/slay.py", line 70, in MenuClick
    EditorWindow(self)
  File "/Users/albertoperrella/Desktop/slay.py", line 85, in __init__
    self.ECanvas.create_image((3,3),image=self.Background,state="normal",anchor="nw")
  File "/Library/Frameworks/Python.framework/Versions/3.1/lib/python3.1/tkinter/__init__.py", line 2140, in create_image
    return self._create('image', args, kw)
  File "/Library/Frameworks/Python.framework/Versions/3.1/lib/python3.1/tkinter/__init__.py", line 2131, in _create
    *(args + self._options(cnf, kw))))
_tkinter.TclError: image "pyimage2" doesn't exist

The two classes are made in a similar way, so I don't know why I get the error with the second one. I am sure that it isn't a writing error e.g.(conttruct instead of construct) and that the images I am using actually exist.
So I think that:

I am making some concept mistakes,
or it is a bug (or subtle behaviour of Tkinter) in python.

A:

I solved myself the problem :
The second class I defined was the problem cause it used another root window, alias Tk(). An equivalent to the normal Tk() window is the Toplevel() that is the same as a root but hasn't its own interpreter context.
Shortly, to solve the problem I had to change the first line of the init() method of the EditorWindow class from
        self.Eenu=Tk()

to
        self.Eenu=Toplevel() 

