Did you try the code I posted ?

As I spent hours to make it finally work, here my working solution:

    my $ua  = LWP::UserAgent->new();
    my $url = "http://your_url";
    my $filename = "d:\\clips\\videoclip.mp4";

    my $response = $ua->post($url,
        ['file' => [ $filename ]],
        'Content_Type' => 'form-data'  # add here more header paramete
+rs if necessary
    );
[download]

And if you switch to single quotes, you can replace the double backslashes by single ones:

my $filename = 'd:\clips\videoclip.mp4';
[download]

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

#!/usr/bin/perl -w

use LWP::UserAgent;
use JSON;
use Encode;
use utf8;

my $ua = LWP::UserAgent->new;
$ua->timeout(10);
$ua->env_proxy;
my $url = "xxx";
my $token = 'x';
my $sign = 'xxxxx';
my $file = '/home/xxx/xxxxxxxxxx.jpg';
my $response = $ua->post($url,
                        ["token" => $token,
                         "sign" => $sign,
                         "image" => [$file]
                        ],
                        'Content_Type' => 'form-data');
if ( $response->is_success ) {
    print $response->decoded_content,"\n";
}
else {
    die $response->status_line;
}
[download]

the file param "image" use an Array "$file"