scab or scar

How long can a scab last, really? In August, I scraped my knee across a rock in Malibu. The waves were huge and knocked me over. I didn't see the rock in the water. (Why'd you go during south swell? my sister asked later.) The person I was with didn't care and swam away from me. Afterwards, I sat on my towel and watched it bleed a little. My hand is covering it in the picture. It left a purple scab that I thought would've gone away by now, but there it is. Maybe it's permanent? Nooo!