*) phKeyLowercase does not exist. Perhaps you should be trying phKeyLowerCase?
*) This should generate a list of all the constants that it exports:
#!/usr/bin/perl -wl
package ap;
use Win32::OLE::Const "Adobe Photoshop";
package main;
$, = $/;
print sort grep defined *{"ap::$_"}{"CODE"}, keys %ap::;
Update: Hopped over to a machine that actually has AP on it and discovered that your code still doesn't work. Corrected version included in the readmore.
#! /usr/bin/perl
use strict;
use warnings;
use Win32::OLE;
use Win32::OLE::Const 'Adobe Photoshop';
use File::Spec;
my $image_file = './pic.jpg';
# start photoshop
my $ps = Win32::OLE->new('Photoshop.Application') or die $!;
$ps->{Visible} = 0;
# open image
my $desc = $ps->MakeDescriptor();
my $control = $ps->MakeControlObject();
$desc->PutPath(phKeyNull,$image_file);
$control->Play(phEventOpen,$desc,phDialogSilent);
# autolevels
$desc = $ps->MakeDescriptor();
$control = $ps->MakeControlObject();
$desc->PutBoolean(phKeyAuto, 1);
$control->Play(phEventLevels,$desc,phDialogSilent);
# resize to 400 * 400 px
$desc = $ps->MakeDescriptor();
$control = $ps->MakeControlObject();
$desc->PutUnitDouble(phKeyWidth, phUnitPixels, 400);
$desc->PutBoolean(phKeyConstrainProportions, 1);
$desc->PutEnumerated(phKeyInterfaceIconFrameDimmed,phTypeInterpolation
+,phEnumBicubic);
$control->Play(phEventImageSize,$desc,phDialogSilent);
$control = $ps->MakeControlObject();
my $d1 = $ps->MakeDescriptor();
my $d2 = $ps->MakeDescriptor();
$d2->PutEnumerated(phKeyPNGInterlaceType,phTypePNGInterlaceType,phEnum
+PNGInterlaceNone);
$d2->PutEnumerated(phKeyPNGFilter,phTypePNGFilter,phEnumPNGFilterAdapt
+ive);
$d1->PutObject(phKeyAs,phClassPNGFormat,$d2);
(my $outfile = File::Spec->rel2abs($image_file)) =~ s/\.jpg$/_thumb.pn
+g/;
print $outfile,"\n";
$d1->PutPath(phKeyIn,$outfile);
$d1->PutBoolean(phKeyLowerCase, 1);
$control->Play(phEventSave,$d1,phDialogSilent);
$desc = $ps->MakeDescriptor();
$control = $ps->MakeControlObject();
$control->Play(phEventClose,$desc,phDialogSilent);
