I'd rotate the graphics before-hand and restore afterwards:

#!/usr/bin/perl 

use PDF::API2;

my $img1="../first.gif";
my $pdffile="../sample.pdf";

my $pdf = PDF::API2->new( -file => "$pdffile" );

my $page1 = $pdf->page;
$page1->mediabox('A4');

my $photo1 = $page1->gfx;

my $photo_file1 = $pdf->image_gif($img1);

$photo1->save;
$photo1->transform(
    -rotate    => 45,
    -translate => [my $_x = 100, my $_y = 50],
    );

$photo1->image( $photo_file1,50,360,510,250);

$photo1->restore;

$pdf->saveas($pdffile);
$pdf->end();
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There's likely to also be some translation involved depending on what corner you want to pivot from.