Use the HTTP-API as Gravatar default image

You can use the HTTP API of DiceBear as Gravatar default image. But before that, let's take a look at the conditions for Gravatar default images:

1. ✅ MUST be publicly available (e.g. cannot be on an intranet, on a local development machine, behind HTTP Auth or some other firewall etc). Default images are passed through a security scan to avoid malicious content.
2. ✅ MUST be accessible via HTTP or HTTPS on the standard ports, 80 and 443, respectively.
3. ⚠️ MUST have a recognizable image extension (jpg, jpeg, gif, png)
4. ⚠️ MUST NOT include a querystring (if it does, it will be ignored)

Source: https://de.gravatar.com/site/implement/images/

Since Gravatar does not support SVG, we have to use the PNG endpoint.

JavaScript

const emailHash = encodeURIComponent('00000000000000000000000000000000');
const defaultImage = encodeURIComponent(
  'https://api.dicebear.com/9.x/lorelei/svg'
  'https://api.dicebear.com/9.x/lorelei/png'
);

const gravatarImage = `https://www.gravatar.com/avatar/${emailHash}?d=${defaultImage}`;
// https://www.gravatar.com/avatar/00000000000000000000000000000000?d=https%3A%2F%2Fapi.dicebear.com%2F9.x%2Florelei%2Fpng

PHP

$emailHash = urlencode('00000000000000000000000000000000');
$defaultImage = urlencode(
  'https://api.dicebear.com/9.x/lorelei/svg'
  'https://api.dicebear.com/9.x/lorelei/png'
);

$gravatarImage = sprintf(
  'https://www.gravatar.com/avatar/%s?d=%s',
  $emailHash,
  $defaultImage
);
// https://www.gravatar.com/avatar/00000000000000000000000000000000?d=https%3A%2F%2Fapi.dicebear.com%2F9.x%2Florelei%2Fpng

Usually we set options in the query string, such as the seed. Since a query string is not allowed by Gravatar, the HTTP-API allows you to specify the options in the path. Just replace the question mark with a slash and encode the options.

JavaScript

const emailHash = encodeURIComponent('00000000000000000000000000000000');
const options = `seed=${emailHash}`;
const defaultImage = encodeURIComponent(
  `https://api.dicebear.com/9.x/lorelei/png?${options}`
  `https://api.dicebear.com/9.x/lorelei/png/${encodeURIComponent(options)}`
);

const gravatarImage = `https://www.gravatar.com/avatar/${emailHash}?d=${defaultImage}`;
// https://www.gravatar.com/avatar/00000000000000000000000000000000?d=https%3A%2F%2Fapi.dicebear.com%2F9.x%2Florelei%2Fpng%2Fseed%253D00000000000000000000000000000000

PHP

$emailHash = urlencode('00000000000000000000000000000000');
$options = sprintf('seed=%s', $emailHash);
$defaultImage = urlencode(
  'https://api.dicebear.com/9.x/lorelei/png?' . $options 
  'https://api.dicebear.com/9.x/lorelei/png/' . urlencode($options) 
);

$gravatarImage = sprintf(
  'https://www.gravatar.com/avatar/%s?d=%s',
  $emailHash,
  $defaultImage
);
// https://www.gravatar.com/avatar/00000000000000000000000000000000?d=https%3A%2F%2Fapi.dicebear.com%2F9.x%2Florelei%2Fpng%2Fseed%253D00000000000000000000000000000000