Much better, baklobsters ... your code example now runs (although I would still recommend understanding how to use strict and use warnings).

I've only used the Photo object before to create images in the GUI itself, so I went to Active State's website to find out what they support.  According to their documentation for the Photo object:

    The standard Tk distribution comes with handlers for XBM, XPM, BMP, JPEG, PNG and PPM/PGM formats, which are automatically registered on initialization.

I didn't see anything there about the Window format, or any kind of reference to doing a screen capture.  Are you sure it's supposed to be a valid operation?

If it's a screen capture you need, would you consider doing it with a separate program?  If so, you might want to try The Gimp, which is a very powerful freeware image editor that supports screenshots (single windows and desktop both), and runs great on Windows.