Hide users without profile pics
There's no photo attribute on the UserElementType, so you can't query by it like you're trying.

Completely untested, but you can probably work around that with something like this:

{% if geslacht_param_string !=''  %}

{% set queryParams = {
    search: {
        query: geslacht_param_string,
        attribute: 'geslacht'               
    },
    geboortedatum : dateRange,
    order :'lastName',
} %}

{% else %}
    {% set queryParams = {
        geboortedatum : dateRange,
        order :'lastName',
    } %}
{% endif %}

{% set allUsers = craft.users(queryParams).find() %}

{% set usersWithPhotos = [] %}

{% for user in allUsers %}
    {% if user.photo %}
        {% set usersWithPhotos = usersWithPhotos|merge([user]) %}
    {% endif %}
{% endfor %}

There are {{ usersWithPhotos|length }} users with photos.