This already exists for automatic AI detection with a percentage accuracy, but it doesn't usually include a nightshade indicator. There are also different sites that let you mess with contrast and/or saturation, though not all of them work with URL and no site does all three.
The purpose of the contrast/saturation controls are that it makes noise in the image super visible which can be a dead giveaway for AI, but there is also noise in Nightshade.
Imagine if it had no internet access but it had all the relevant docs.