Drag a box over anything that should not be in the picture — a face, a number plate, a screen, a name on a parcel — and cover it with pixelation, a heavy blur, or a solid black block.
Exporting redraws the picture, so the copy you save carries no metadata at all. For anything that truly has to stay secret, use the solid block: a blur can in principle be undone, and pixelation is guessable when the content is predictable.