Private images are images that are not accessible to any end-user. Since much effort goes into producing an original image, there might be scenarios where original images must be protected and made inaccessible to anyone.
For example, a paid image gallery that shares original images with its customers only when the payment is completed.
However, if there are named transformations specified within the dashboard, these named transformations can be used to transform your images. Named transformations can be used with private images without generating a valid signed URL.