A fairly large (say 5 feet tall) and robust robot is equipped with a video camera, some image processing software and a speaker. When it detects an individual dropping litter, it follows them for five minutes or so admonishing them about their selfish ways, unless they pick up the litter.
are two versions, polite and not so polite. Polite's phrases would be suitably middle-classed, something like:
"This person is a litterer! They are selfish and self-centered and are ruining your environment!"
"Pick that up - would you do that at home?"
"This place looks like a pigsty thanks to you!"
"Keep your country tidy!"
The not so polite version would be a little more earthy, useful for the rougher areas of town:
"Oi! You dropped litter you ****!"
"Come back here and pick up your s**t, you ****, I don't want to have to wade through your crap!"
"Think you're ****ing clever do you? If I was human I'd ram that litter up your ****!"
Advanced versions would have a battery of sensors, such as kebab-fat sniffers, burger-wrapper spotters, stale beer smellers and loud music detectors to guide them to areas more likely to be littered.