How to scan an old photograph

A photographic print holds roughly as much detail as 600 DPI records. Scanning a standard snapshot at 1200 DPI gives you a file four times the size in which you can see the paper fibres more clearly, and the picture no better.

There are two exceptions. A small print you intend to enlarge — anything under about three inches on its long edge — is worth 1200 DPI, because you are going to ask more of those pixels than the original ever had to give. And negatives and slides need 2400 DPI or more, because you are scanning something the size of a postage stamp.

If your scanner offers a 'photo enhancement', 'descreen' or 'dust removal' setting, turn all of them off. They soften the surface, and a soft scan cannot be un-softened later.

Cropping is easy afterwards and free. Recovering an edge you cut off at scan time is not possible at all, and old prints carry information at their edges — a photographer's stamp, a date printed in the border, a deckled edge that dates the paper.

Where the print is torn into pieces, lay them all down in one scan in roughly the position they belong. One scan of two halves keeps the alignment; two scans throws it away.

TIFF if the software offers it: it stores every pixel and stays legible in thirty years. A JPEG at maximum quality is close enough that nobody could pick it out by eye, and it is a quarter of the size.

What matters more than the format is that you keep the scan you made rather than the copy you edited. Everything else can be redone from the original scan; nothing can be redone from a resaved JPEG.

A phone photograph of a print is a real option, and for a framed photograph that will not come out of its frame it is the only one. It wants flat daylight — near a window, not in direct sun — no flash, the phone held parallel to the print rather than at an angle, and your own shadow out of the frame.

The failure to avoid is the angled shot that turns a rectangle into a trapezoid. Straight above, or as near as you can manage.

This is the only step people skip that costs them something. A speck of dust on the platen appears on every photograph in the batch in exactly the same place, and it is indistinguishable from a mark on the print.

A blower and a lint-free cloth at the start of each session. If you have just scanned something moldy, clean the glass before the next one.