I have found the problem.

An empty photo object must be set without explicit
descriptor, nor image tags.
So in the main window, the line:

my $image = $label ->Photo('image',
                     -height => 10, 
                     -width => 10,
                     -format=>'XPM');
[download]

become:

my $image = $label ->Photo(
                     -height => 10, 
                     -width => 10);
[download]

Nice day for you all!