gistfile1.php

<?php

$fields = array(
  'file_name' => "wallpaper.jpg",
  'content-type' => "image/jpg",
  'content' => '"'.base64_encode(file_get_contents("./wallpaper.jpg")).'"'
);

$fields_string = json_encode($fields);

echo $fields_string;

echo "\n\n";

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://yoursite.desk.com/api/v2/cases/1/attachments");
curl_setopt($ch, CURLOPT_PORT, 443);
curl_setopt($ch, CURLOPT_TIMEOUT, 15);
curl_setopt($ch, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT']);
curl_setopt($ch, CURLOPT_USERPWD, "email:password");
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, $fields_string);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type: application/json',
    'Content-Length: ' . strlen($fields_string)
  )
);

$return = curl_exec($ch);
echo $return;
exit;