Wikipedia: KH-11 KENNEN Resolution and ground sample distance
A perfect 2.4-meter (94 in) mirror observing in the visual spectrum (i.e. at a wavelength of 500 nm) has a diffraction limited resolution of around 0.05 arcsec, which from an orbital altitude of 250 km (160 mi) corresponds to a ground sample distance of 6 cm (2.4 in). Operational resolution should be worse due to effects of the atmospheric turbulence.
This references
Fried, D. L. (October 1966). "Optical Resolution Through a Randomly Inhomogeneous Medium for Very Long and Very Short Exposures". Journal of the Optical Society of America. 56 (10): 1372–1379.
An appropriate Gaussian blur on the image might have made it more believable.
One of the interesting things about SpaceX's 'Starship' is that, if successful, it will be able to carry substantially larger diameter mirrors into orbit (payload bay is 8 metres in diameter) , enabling the taking of higher resolution images from orbit. That said, large monolithic mirrors are both difficult and expensive to manufacture, so it probably makes more sense to produce a segmented mirror like the James Webb Space telescope, and add adaptive optics - which the Starship could happily carry with its vast payload capacity. A seven metre aperture on a mirror gives a theoretical best ground sample distance of roughly 2.5 cm.
Of course, aircraft don't fly at 250km altitude, and can use smaller aperture optics with image stabilisation and adaptive optics to get good images. U2s are not the only examples of this. Flying directly over a Russian airbase might not be a good idea.
I think KH-11 Kennen images in reality end up with a 10-15cm ground sample distance.
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Edited to get the quote formatted correctly.