There are many ways to scan photos and all are good techniques however, there are several important things to consider when scanning photos. They are:
1. Quality of original.
2. File size of scanned output.
3. Do you need to enhance the photo.
4. Will the scanned photo be enlarged for printing or viewing on CRT.
5. Color or Black & White.
If the quality of the original photo is in perfect or very good condition you may consider scanning at a lower DPI because there are no imperfections in the photo to be picked up by the scanning process.
Storage space should be considered for the final product of your picture files. TIF formats require more storage space than JPG files. Depending on your graphics software and word processors, there are some graphics that certain software packages will not handle. Progressive JPG is NEVER a good idea for storing photos - they require more space, some picture quality is lost in the saving process, and some word processors will not work with progressive JPG files.
After scanning a photo, will you desire to enhance the photo at a later date? If that is a possibility, and you are storing your files as a jpg file, ALWAYS open your jpg file and save it as a TIF file and do your enhancing with the TIF file. When you have the photo enhanced to your satisfaction, then resave it as a jpg file to conserve space and delete the work tif file. The reason for this is because each time you open and resave a jpg file, small portions of the quality of the graphic will be lost. This does not occur when working with tif files.
Will your scanned photos be enlarged for viewing either on your CRT and especially for printing? If so I suggest you scan at at least 400 DPI or higher. The higher DPI you use for scanning, the better the photo will look when enlarged.
Many "Experts" (?) in graphics will tell you that there is no need to scan over and above the DPI of your CRT, and/or printer. We deal in many many graphics and I am here to tell you that is pure BULL!
Don't take our word for it -- try different things yourself. Try scanning a small photo at 100 DPI - enlarge it and print it or look at it on your CRT. Then scan the same photo at 400 DPI or higher - enlarge it, and look at it again. You will see what I mean.
Color files take much much more storage space. Do you really want to scan and save a photo in color? Digital photography is realtive new and I may be incorrect, but I suspect a printed color photo will fade in time just as regular photographs do sometimes. If you do not specifically desire color photos, scan in black and white. The files will be smaller, AND the photo will look better, especially if the original was an old photo.
Try this ! Take a photo that has been scanned in color and change the data type over to 8 bit grayscale. You will see a much better photo in quality of the image, and when you compare file size, you will also see a vast difference.
Reguardless of how you scan - color or B & W - once you have enhanced the photo to your satisfaction, you can save even more storage space by resampling , and/or resizing the photo to a smaller size, generally without destroying any or very little of the enhanced quality of the photo.
Finally, if the original is a very dotty photo - i.e. newspaper, etc., the lower the DPI the better the scanned output - usually, yes, usually, but at times that will not hold true.  . In these cases, experimentations are the rule of thumb.
Remember !!! Cameras and scanners see many things our eyes do not see.