Autonomous cars may be the future, but it'll be decades before not owning a car really takes off. Maybe for single people or couples without kids it will be possible, or those times you don't have the kids, but for the rest of us it's just not feasible.
The amount of junk you carry seems to scale in proportion to the convenient carrying capacity of your transportation. If you have a huge SUV of course it will be packed with all kinds of stuff. If all you have is a stroller you'll scale back accordingly.
"There's no way that'd be possible" is utter defeatism. Somehow as a species we survived for tens of thousands of years before cars. I doubt autonomous cars won't be embraced by millions just because you personally find them inconvenient.
A slightly customer-friendlier option would be to take the picture every time the car is vacated, and then clean (and charge) when the detritus reaches a certain level. After all it wouldn't be right to penalize people who are simply in too much of a hurry to care about previous travelers' candy wrappers.
If the vehicle is detected as being "messy" it can swing back to the depot for a cleaning or have someone dispatched to clear it out.
There are many reasons why you'd want to own a car, but the number of reasons for you to need to own a car plunges dramatically when the quality offered by shared rides meets or exceeds the experience your average car-owner has.
Imagine a car that always has sufficient fuel or battery power to get you where you're going, that is clean every time you use it, that never has to be parked, that comes reliably within minutes of being summoned, and never, ever has to be taken in to the garage to be fixed.
That's the future if things come together as they should.
Rich people will own their own cars, probably several of them, but your average person won't see the need. If they want to splurge they'll rent a car solo. If they want to save money, ride-share with a few others.