If you have them on paper, the ideal is to scan them: at 300 dpi or more, saving as TIFF or PNG (not JPG, to avoid compressing twice). A standard desktop scanner is fine.
If you don't have a scanner, photograph with your phone straight on, without flash, in natural window light, and try to keep the photo as flat as possible. Take 2-3 shots in case one is blurry.
What you shouldn't do: trim, flatten or run them through apps like Remini or enhancers before sending them to us — that destroys detail and leaves us without the original information to work from.
If you'd rather skip all this, you can also send us the paper photos: we scan them and return them exactly as they came.