I'm not sure if Imager can use macfonts? Have you tried postscript fonts? I used ttf fonts in the past without any problems though.

On Imager::Font I found something to check if Imager is t1 or truetype capable:

use Imager;
  print "Has truetype"      if $Imager::formats{tt};
  print "Has t1 postscript" if $Imager::formats{t1};
  print "Has Win32 fonts"   if $Imager::formats{w32};
  print "Has Freetype2"     if $Imager::formats{ft2};
[download]

I also found some link that's about Imager and .dfonts. It claims you need to add:

my $font = Imager::Font->new(file=>$font, type=>ft2) or die Imager->er
+rstr;
[download]

Good luck ;)