To see how it's done in an xls, fire up the macro recorder in Excel then insert your image. Now move the image. Stop the macro recorder and open up Excel's VBA IDE. Take the generated code and convert it to perl.

use strict;
use warnings;
use Win32::OLE;

my $excel = Win32::OLE->CreateObject('Excel.Application');
$excel->{Visible} = 1;

my $wb = $excel->Workbooks->Add;
$wb->ActiveSheet->Pictures->Insert( "C:\\s\\x.png" )->Select;
$excel->Selection->ShapeRange->IncrementLeft( 40 );
$excel->Selection->ShapeRange->IncrementTop( 40 );

__END__
Sub Macro1()
' Macro recorded with Macro Recorder
' Tools -> Macro -> Record new macro
    ActiveSheet.Pictures.Insert( _
        "C:\s\x.png").Select
    Selection.ShapeRange.IncrementLeft 40
    Selection.ShapeRange.IncrementTop 40
End Sub
[download]