I don't think there already exists a module for this.
What you need to do is implement hook_user_update() and check if the user now has a picture assigned but didn't before. If so, use userpoints_userpointsapi() to grant the user the number of points you want.
Something like this:
<?php
function yourmodule_user_update(&$edit, $account, $category) {
if (!empty($edit['picture'] && empty($account->picture)) {
$params = array(
'uid' => $account->uid,
'points' => 10,
// You probably want to provide additional arguments,
// refer to the API documentation.
);
userpoints_userpointsapi($params);
}
}
?>