Previously described bash script allows for uploading a file to PicasaWeb only. With the following (simplified) Perl script one can upload pictures as well as upload with metadata (title description and tags) or create/list albums:

#!/usr/bin/perl

use strict;

use LWP::UserAgent;
use Getopt::Long;
use File::MimeInfo;
use XML::LibXML;

my $AlbumId ="6170354040646469009";
my $profileID="default";

my $Action = 'u'; ## x| u | c | l (default action is Upload)
my $entryTitle = ''; my $entryDescription = '';
my $entryKeywords = '';
my $ActionUpload =''; my $ActionList = '';
my $ActionCreate = ''; my $ActionXload = '';
my $ImageFile = '';
my $dummyReq='';

GetOptions("xload" => \$ActionXload, "upload" => \$ActionUpload,
  "list" => \$ActionList, "create" => \$ActionCreate,
  "title=s" => \$entryTitle, "description=s" => \$entryDescription,
  "keywords=s" => \$entryKeywords,
  "file=s" => \$ImageFile,
  "album=s" => \$AlbumId, ## UploadFile to Album
) ;

## Determine action:
if ( $ActionUpload ) {$Action = 'u'} elsif ( $ActionList ) { $Action = 'l'}
elsif ( $ActionCreate ) { $Action = 'c'}
elsif ( $ActionXload ) { $Action = 'x'}

OAuth 2.0 authorization is handled with Python script oauth2picasa.py. The script is an adapted/copy-pasted fragment of code borrowd from picasawebsync:

### Authenticate with external script (oauth2picasa.py):
my $ACCESS_TOKEN=`oauth2picasa.py`;
chomp($ACCESS_TOKEN);
print STDERR "*** AccessToken: $ACCESS_TOKEN [AlbumId: $AlbumId]\n";

my $req ; my $blog_entry ;

my $picasawebURL = "https://picasaweb.google.com/data/feed/api/user/$profileID";

if ( $Action eq 'c' ) {## Action: create album
  $req = HTTP::Request->new(POST => $picasawebURL );
  $req->header( 'Content-Type' => 'application/atom+xml' );

  $blog_entry = "<entry xmlns='http://www.w3.org/2005/Atom'
     xmlns:media='http://search.yahoo.com/mrss/'
     xmlns:gphoto='http://schemas.google.com/photos/2007'>"
  . "<title type='text'>$entryTitle</title>"
  . "<summary type='text'>$entryDescription</summary>"
  . "<media:group><media:keywords>$entryKeywords</media:keywords></media:group>"
  . "<category scheme='http://schemas.google.com/g/2005#kind'
     term='http://schemas.google.com/photos/2007#album'></category></entry>";

    $req->content($blog_entry);
} 
elsif ( $Action eq 'l' ) {## Action: list albums
  $req = HTTP::Request->new(GET => $picasawebURL );

} 
elsif ( $Action eq 'u' ) {## Action: Upload 1 photo w/o metadata
  my $mimeType = mimetype($ImageFile);

  ## https://developers.google.com/picasa-web/docs/2.0/developers_guide_protocol
  $req = HTTP::Request->new(POST => "$picasawebURL/albumid/$AlbumId" );
  $req->header( 'Content-Type' => "$mimeType" );
  $req->header( 'Slug' => "$ImageFile" );

  ## http://www.perlmonks.org/?node_id=131584
  open(FILE, $ImageFile);
  $req->content(join('',<FILE>));
  close(FILE);
}

To upload the binary image data along with its metadata, use MIME content type "multipart/related"; send photo metadata in one part of the POST body (Content-Type: application/atom+xml), and binary-encoded image data in another part. This is the preferred approach according to Picasa Web Albums Data API Picasa Web Albums Data API

elsif ( $Action eq 'x' ) {## Action: Upload 1 photo with metadata
  # https://groups.google.com/forum/#!topic/google-picasa-data-api/2qRfP0EIFhk
  my $mimeType = mimetype($ImageFile);

  $req = HTTP::Request->new(POST => "$picasawebURL/albumid/$AlbumId" );
  $req->header( 'Content-Type' => "multipart/related" );

  open(FILE, $ImageFile);
  my $add_photo_metadata = "<entry xmlns='http://www.w3.org/2005/Atom' 
     xmlns:media='http://search.yahoo.com/mrss/'>"
  . "<title type='text'>$entryTitle</title>"
  . "<summary type='text'>$entryDescription</summary>"
  . "<media:group><media:keywords>$entryKeywords</media:keywords></media:group>"
  . "<category scheme='http://schemas.google.com/g/2005#kind' 
     term='http://schemas.google.com/photos/2007#photo'></category></entry>";

  my $add_photo_data = join('',<FILE>); close(FILE);

  ## http://www.perlmonks.org/?node_id=131584
  $req->add_part(HTTP::Message->new(['Content-Type'
      => 'application/atom+xml'], $add_photo_metadata));
  $req->add_part(HTTP::Message->new(['Content-Type'
      => "$mimeType"], $add_photo_data));
}

$req->header( 'Authorization' => "Bearer $ACCESS_TOKEN" );
$req->header( 'GData-Version' => '2' );

## ### ###
my $res ;
my $ua = LWP::UserAgent->new;

$res = $ua->request($req);

if ($res->is_success) {
   my $decoded_response = $res->decoded_content;
   print "*** OK *** $decoded_response\n";
}

Usage:

Upload with metadata

picasaweb.pl -xload -title PICTURE-TITLE -descr DESCRIPTION \
  -keywords 'TAG1,TAG2' -file FILE.jpg -album ALBUMID

Upload w/o metadata:

picasaweb.pl -upload -file FILE.jpg -album 12345

Create album:

picasaweb.pl -create -title ALBUM-TITLE -descr DESCRIPTION \
   -keywords 'TAG1,TAG2'

List album:

picasaweb.pl -list

Source code: picasaweb.pl