'dict' object has no attribute 'pk' Django Rest API Framework

Im using Django Rest API Framework, I want to upload multiple images for a single project using Angular js.

Here's my model:

class Project(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)
    owner = models.ForeignKey(User)
    number_of_photos = models.IntegerField()

class Photo(models.Model):
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)
    images = models.ImageField(upload_to='photos/', max_length=254)
    project = models.ForeignKey(Project)

I have this serializers:

class ProjectSerializer(serializers.ModelSerializer):
    class Meta:
        model = Project
        fields = ('id', 'created', 'number_of_photos', 'owner')

    def create(self, validated_data):
        project = Project.objects.create(**validated_data)
        return project

class UploadSerializer(serializers.ModelSerializer):
    project = ProjectSerializer(many=True, read_only=True)

    class Meta:
        model = Photo
        fields = ('url', 'created', 'images', 'project')

In my view I got this inside my viewsets.ModelViewSet

serializer = UploadSerializer(data=photo_array, many=True, context={'request': request})

if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=status.HTTP_201_CREATED)

The variable photo_array contains:

[{'project': u'1', 'images': {u'name': u'test-image.png', u'lastModifiedDate': u'2015-04-22T08:51:11.000Z', u'webkitRelativePath': u'', u'lastModified': 1429692671000, u'type': u'image/png', u'size': 43152}}, {'project': u'1', 'images': {u'name': u'test.png', u'lastModifiedDate': u'2015-04-08T08:35:17.000Z', u'webkitRelativePath': u'', u'lastModified': 1428482117000, u'type': u'image/png', u'size': 127433}}]

But it gives me an error 'dict' object has no attribute 'pk'

Did my photo_array variable cause this problem?.