A bit blurry but it looks like leaf gall. I say this because they look raised above the leaf surface. If your camera has a closeup feature take one leaf off, place it on a table, hold the camera very steady with the support of the table and snap a close up photo of the leaf. Galls can be induced by certain mites or wasps. The other possibilities are fungus or virus

I hope this walnut tree isn't close to the house in the ground as they grow to a Height and spread of 30m (100ft) 15m (50ft). Just thought I'd mention it :o))