My partner has them on one of his legs, one large one right across the back which appeared after he stepped awkwardly on a kerb and tweaked his ankle. The doc told him it will never go away.
Looks like a cluster of telangiectasias (spider veins) to me. Smaller than varicose veins and they sit on the top surface of the skin. I used to be a PA for a group consultant dermatologists. But this is only my best guess.