[Florin_Andrei]

Jupiter, Venus, Sirius and, at the very limit, even Canopus are visible with the naked eye during the day. It's just hard to "get a lock" on them because contrast is so low. But if they are close to a large, fixed, easily visible reference (the Moon, a tall building, a tree) then suddenly they pop into view. The first two are easy, the third is doable in good conditions, the last is difficult and requires excellent conditions and a keen eye.

You need more than a few stars for navigation, of course, but I would assume with a good sensor, proper filtering, and nice optics, a computer could see enough stars during daytime to perform navigation.