My photo resolution is too low, how can I make them a higher-resolution?
You will need to re-scan your photos at bigger sizes and higher resolutions.
For example, if the photo was originally scanned at a 3" x 1" size and 150 d.p.i. resolution, you will probably want to scan your photo to a 6" x 2" or 12" x 4" size, and at least 300 d.p.i. resolution.