Those are actually prop vortices. They become visible because of a sudden change in pressure caused by the moving propeller which causes the moisture in the air to briefly condense and become visible. If the air is very dry, you'll never see them. In England it is seen more often. You can also see vortices emanating from wing tips, and sometimes the entire wings are enveloped making you think you're flying through cloud if you are inside the aircraft. That's what is happening in the last photo.

Wayne