The image distance is taken to be negative for which kind of image?

1. The sign convention runs the other way for the second type. 2. The image distance is positive for a real image. 3. It is negative for a virtual image. 4. The sign therefore encodes which side of the lens the image lies on. _Source: OpenStax College Physics for AP Courses 2e (CC BY 4.0), Ch 25 'Geometric Optics', sections 25.1-25.7_