Most likely there's a stone between the brake pad and the brake disk. You can already see a quite nasty scratch on the brake disk. Alternatively, the stone could be between the back plate and the brake disk. Jack up your car, take the wheel off and try to remove debris. If your car does not come equipped with a jack, driving might remove it eventually.
Had this happen on an old Mazda 5 whilst towing on way to holiday.
Some spirited use of the brake assisted in removing said article within about 5 miles.
Other than that it will be wheel off, caliper loosened and pad out to remove.
Normally caused as the front of most pads has a slight taper which directs stones inbetween disc and pad.
Not help as in these you don't use the brakes much due to regen.