How does the scan quality of a photo affect the fairies, you might ask. Well, observe the following three examples of the same photo scanned at three different quality levels (measured in DPI, or "dots per inch"):
Scanned at 300 DPI:
Scanned at 600 DPI:
See the difference? At 600 DPI, you can see the individual strands of the hat decoration, folds in fabric, even the hat pin to the left. More details, when it comes to historical artifacts, are always better. You owe it to future generations to give them all the details you possibly can.
Also, just for fun, here's how a photograph taken with a digital camera compares:
If you're a skilled photographer with quality equipment, you could get a better reproduction than with a basic point-and-click digital camera, which the above is representative of. And, sometimes size and fragility limit what you can put in a scanner bed, and in that case you may have to get by with a photograph; but whenever possible, scan the photo (at 600 DPI or more!)
Here are some other points that the pixel fairies would like you to take away from this tutorial:
Lossy versus lossless formats. Make sure that your master digital back-up photo is saved in a lossless (that doesn't lose quality) format such as TIFF or PNG. These files take up more space, but are vital for retention of detail. You can save copies in alternate lossy (that lose quality) formats, such as JPG, that take up less space and are easier to share between relatives. However, always have the master lossless scan on hand to share with detail-minded cousins!
Cropping photos. I use a straighten tool to get all edges at 90 degree angles, and then crop to the edge of the photo or mounting paper, even if the photo doesn't go all the way to the edge. The edge material might have useful information on the photographer's name and city; decorative designs on a cabinet card might provide hints for dating the photo. If there is anything on the back of the photo (whether a studio mark or a hand-written note by a previous owner), scan that, too!
A note on restorations: With current technology it is quite easy to digitally repair tears, creases, stains, etc. on old photos by using tools in graphic editing programs. It's fine to create a touched-up version for display, but be sure to save a digital backup of the unaltered version and preserve it carefully. The thing with restorations is that you can guess at the details, but you cannot know exactly what the missing pixels are supposed to be. Case in point: in my grandparents' wedding portrait, there was a big ugly spot on Grandma's face. I edited out that blemish as soon as I had scanned it. Time went by, and I ran across different prints of the same portrait, and I realized that each one had the exact same spot. I finally realized that this dirt was actually a polka dot on the tulle veil! That was an historical detail that I had irreverently left on the cutting room floor--so do keep the unaltered image in your archive.
You cannot "retrieve" lost quality. Graphics programs may let you change the DPI setting of a photo. Don't be fooled by this. The max DPI can only be gained through the original scan. Setting a "higher DPI" later on will result in a very poor attempt by the program to fill in the quality holes. It won't work.
Storing your digital photos. Do an internet search for "genealogy digital backup" (or any similar phrase) for lots of ideas on how to store your files to protect against loss, such as backup drives and internet storage. It's a good idea to have multiple backups in case one fails! Myself, I have copies on my hard drive, saved to my Ancestry.com tree, and organized in Flickr albums. I enjoy the organization features in Flickr, and you get a ton of space for free (1 TB) plus privacy features (you can choose who can see your photos). Choose at least 2-3 backup methods that make sense to you.
Storing the original photos. Look for acid-free paper, photo boxes, plastic sleeves, etc. Acid-free is the key! Like with digital storage, there are different options--mounting on paper pages in an album, keeping in plastic sleeves in a 3-ring binder, or stored in photo boxes. Find one that works for you; just make sure that all parts of the storage system are acid-free.
A closing request from the fairies: they are also often traumatized to the point of death by photocopies. I know that sometimes a photocopy is all that has been passed down to us, and we don't know which distant relation (or antique store) holds the original. But the fairies request that you please try your hardest to track down that original print and distribute your high-quality scan for the viewing pleasure of all family members.
Please e-mail me if you have questions (or corrections). I'm passionate about preserving old photographs, and I would love to provide whatever tips I am able to get you started on your preservation project.