Django Rest Framework with easy-thumbnails

Best solution is probably to subclass serializers.ImageField() and use the the code you found in the to_representation method (docs for custom fields). Your field could then look like this:

from easy_thumbnails.templatetags.thumbnail import thumbnail_url

class ThumbnailSerializer(serializers.ImageField):

    def to_representation(self, instance):
        return thumbnail_url(instance, 'small')