Still Images : Archive
An archived image file should be as close as possible to its original form (i.e. minimal compression, format changes, etc.) and should be stored on some durable or secure (i.e. backed up) medium. For still images archive we recommend backing up a high quality .tiff, or photoshop working file.
Always keep the original image with its original size and dpi (dots per inch). The image can always be downscaled later, but it cannot increase in size without losing quality.
For scanned images a minimum resolution of 150 dpi is good. 300dpi is better.
Standard format: .TIFF, or .PSD (Photoshop working file)
Archive option #1: Backup on flash drive or hard drive.
Tutorial: Saving to a flash drive or hard drive
Archive option #2: Backup image file to a CD/DVD.
Tutorial: Saving to a data CD/DVD
Tutorial: Formatting an external device for Mac