What distinguishes a decorative screen from a privacy screen?
Well, a privacy screen can be decorative but a decorative screen may not necessarily give you privacy.
The main consideration is the screen opacity. Many councils will specify a minimum opacity of 75% as being a privacy screen.
Anything less than this must be described as purely decorative.
Take the 2 images below. The leaf pattern has an opacity value of about 76% while the Moroccan pattern has an opacity value of about 50%.
Both are decorative screens but only the leaf pattern, could be described as a privacy screen.