where did that come From?

Bryony West took a picture of her daughter one halloween dressed up as a witch with her very own pet spider.

When the photograph came back somehow a real image of a spider had appeared on the bottom left hand side of the picture. This was back in the days of photo processing, so, Is it a poor unfortunate spider that got caught in the process of the photo developement or a ghostly spider making an appearence in the photo?