There's an app where you can have a seeing person help you. I think its meant for shopping and navigating places but I don't see why they couldn't be used as paper checkers
This whole thread is nothing but jokes. The real answer is they wipe their butthole with their finger and then press their fingers together to feel if it's at all sticky.
Get yourself a travel bidet <$20 on Amazon, and start with that. You use warm tap water from your commode.
No installation, but a bit of practice.
My proctologist ranted about general bad wiping habits in the US that damage the hemorrhoid tissue over time. Don't spend your life in sin and misery as I have in the House of the Rising Sun, and stick to only dabbing with bathroom tissue, and use bidets to do the heavy cleaning.
Lot of jokes here, my brother repeatedly has told me he is disgusted by the fact that we look at toilet paper to tell if we are clean. Granted he would have to get the TP very close to his face to be able to see anything. He says he just wipes until he is clean. Not an exciting answer, but that's what I got.
I have a live feed camera in my toilet. Every time I take a shit, I get out my phone and watch the footage so I can inspect both the turd and my asshole and plan my wiping strategy accordingly.