Exclude entries by array of authors from ElementCriteriaModel
Iterating on Michael's answer: build an array of users to exclude, like this:

{% set excludeArray = null %}
{% for user in entry.winners_exclude %}
    {% if loop.first %}{% set excludeArray = ['and'] %}{% endif %} {# only set this array if exclude users exist #}
    {% set excludeArray = excludeArray |merge(['not ' ~ user.id]) %}
{% endfor %}

{# check if users should be excluded, I'm not sure what happens if you'd do .author(null) #}
{% if excludeUsers %}
    {% paginate craft.entries.section('bildupload').author(excludeUsers) %}
{% else %}
    {% paginate craft.entries.section('bildupload') %}
{% endif %}