Problems with Image Link

I created a model called worker that has a field called signature where I'm uploading the signature digital in an image:

class Trabajador(models.Model):
    usuario = models.OneToOneField(User)
    dni = models.CharField(max_length=8,primary_key=True)
    apellido_paterno = models.CharField(max_length=50)
    apellido_materno = models.CharField(max_length=50)
    nombres = models.CharField(max_length=100)    
    firma = models.ImageField(upload_to='firmas')
    estado = models.BooleanField(default=True)

    def nombre_completo(self):
        return self.apellido_paterno+' '+self.apellido_materno+' '+self.nombres    

    def __str__(self):
        return smart_str(self.apellido_paterno)+' '+smart_str(self.apellido_materno)+' '+smart_str(self.nombres)

I have a form named TrabajadorForm where I use the model created previously:

class TrabajadorForm(forms.ModelForm):

    class Meta:
        model = Trabajador
        fields =['dni','apellido_paterno','apellido_materno','nombres','usuario','firma']

    def __init__(self, *args, **kwargs):
        super(TrabajadorForm, self).__init__(*args, **kwargs)
        for field in iter(self.fields):
            self.fields[field].widget.attrs.update({
                'class': 'form-control'
        }) 

I have a view to be able to modify the worker:

class ModificarTrabajador(UpdateView):
    model = Trabajador
    template_name = 'modificar_trabajador.html'
    form_class = TrabajadorForm
    success_url = reverse_lazy('administracion:maestro_trabajadores') 

And the template called modify_worker:

{% extends "base_administracion.html" %}
{% block cuerpo %}

<div class="row">
    <div class="col-lg-12">
        <h1 class="page-header">Modificar Trabajador</h1>
    </div>    
</div>
<div class="row">
    <div class="col-lg-12">
        <div class="panel panel-default">
            <div class="panel-heading">
                Por favor ingrese todos los campos necesarios.
            </div>
            <div class="panel-body">
                <form role="form" action="{% url 'administracion:modificar_trabajador' trabajador.pk %}" method="post" enctype="multipart/form-data">
                    {% csrf_token %}
                    <div class="form-group">
                        {{ form.as_p }}                         
                    </div>  
                    <div class='form-group'>
                        <input type="submit" class="btn btn-primary" name="submit" value="Modificar Trabajador">
                        <button type="reset" class="btn btn-primary" onclick="location.href='{% url 'administracion:maestro_trabajadores' %}'">
                            Cancelar
                        </button>
                    </div>
                </form>         
            </div>
        </div>
    </div>
</div>
<div id="popup"></div>
{% endblock cuerpo %}

Until then everything works very well but when I click on the signature link I get an error because the link points to:

  

link

and not to the correct location of the file, I would like to see if something can be done to solve this problem. Greetings.