IMAGE FORMATS
    The photo image code is structured to allow handlers for additional
    image file formats to be added easily. The photo image code maintains a
    list of these handlers. Handlers are added to the list by registering
    them with a call to Tk_CreatePhotoImageFormat. The standard Tk
    distribution comes with handlers for XBM, XPM, BMP, JPEG, PNG and
    PPM/PGM formats, which are automatically registered on initialization.

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    Usually this will find the correct handler, but if it doesn't,
    the user may give a format name with the -format option to
    specify which handler to use. 

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my $img = $mw->Photo(-data => $data);