my %image_data_for = (
    A => {
        name => 'ImageA',
        data => $LtrA,
    },
    B => {
        name => 'ImageB',
        data => $LtrB,
    },
); 

# Image A holder in Main Window
$mw->Label(-text => 'Image A:')->pack();
my $cvsA = $mw->Canvas(-background=>'yellow', -height => 40, -width => 40)->pack();

# Image B holder in Main Window
$mw->Label(-text => 'Image B:')->pack();
my $cvsB = $mw->Canvas(-background=>'green', -height => 40, -width => 40)->pack();

# Set Image A
create_canvas_image($cvsA, $image_data_for{A});

# Button to make Image B
$mw->Button(
    -text => 'Add Letter B',
    -command => [\&create_canvas_image, $cvsB, $image_data_for{B}],
)->pack(-pady => 5);

MainLoop;

sub create_canvas_image {
    my ($canvas, $image_data) = @_;

    my $img = $mw->Photo($image_data->{name}, -data => $image_data->{data});
    $canvas->create('image', 30, 30, -image => $img);
}