This solution will work fine. A textvariable can be used just like any other variable. If you change it, the display is automatically updated (no need for "edit" commands).

As a small enhancement, I show how to use the "filetypes" filter. If the op wants to pass a ref to the textvariable, I show how to do that also although if this is a special purpose routine, I would have no problem with just accessing the $ImageFilePath directly without going through a reference. I also tend not to declare var names that aren't used again (like the LHS of button creation).

# entry textbox for Image times dialog 
my $entImageFile = $mw->Entry(-width=>30, 
                              -textvariable=>\$ImageFilePath,)->pack()
+; 

# button to browse for file 
$mw->Button( -text=>'Browse', 
             -command=> sub { openImageFileDialog(\$ImageFilePath)},
            )->pack(); 

MainLoop; 

sub openImageFileDialog 
{ 
   my $path_ref = shift;
   my @types =
       (["Image Files", [qw/.bmp .giff .tiff/]],
        ["All files",        '*'],
       );

   $$path_ref = $mw->getOpenFile(-title => 'Open Image File:',
                                 -filetypes => \@types);
}
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