It really depends on what you mean by "looooong". Wall of text below:
TL/DR:
There isn't a really easy bulletproof way to do this and maintaining digital copies requires lots of diligence over time.
Just for kicks...if you want these to be around 500 years from now...
Printed books remain a far superior to digital media for long time archiving as long as they are stored securely in environmentally controlled conditions. Your safest bet bet for "looooong" term storage would be to convert the data to ASCII, binary, etc. and print them as a book on a long term storage media, catalog the books and store them in the aforementioned conditions. You'll also need a key book to explain what format the files are, how to read them and how to recompile them. Eventually JPEG, TIFF, etc. will be unusable formats. You could also have the data engraved on metal or something like that instead of paper. Think of the disc on the
Voyager space craft golden record.
Now actually being realistic...
My gut says Gordo is right but physical prints have the disadvantage of being hard to index and depending on the size of the photos scanning them back to a digital format will be very painful. They are also susceptible to environmental damage in ways that digital is less so. If the data is REALLY important my suggestion retain both a digital, physical digital and physical printed copy. Physical digital media (discs, disks, etc.) all have a lifespan and will need diligence to maintain. Digital media file systems and file formats will eventually be hard to utilize as they age.
On physical "prints":
For the physical copy make sure that archival quality media (ink, paper, etc.). This very much depends on how you "print" them.
On digital (basically all of this snow balls with each bullet point):
- File formats don't last forever. Eventually TIFF, JPEG, etc. will go the way of the dinosaur. You'll have to have some kind of antique emulation technology to recover them. Think of this in the vein of trying to read a middle-english book. So every 10 years or so you'll need to verify that the format is still relevant and if not likely convert the files.
- File systems don't last forever. FAT, NTFS, HFS, etc. will eventually go away. You may have a hard drive recovering files at a later date. So every 10 years or so you'll need to verify that the file system is still relevant and if not likely migrate the files.
- Redundant array of inexpensive/indpendent disks, commonly known as RAID Arrays are great for short-medium term data storage. Sometimes configured and attached to a network becoming a Network attached storage (NAS).
- RAID also has different configurations (pcmag.com). Each with its own complexities and redundancies.
- Spinning disk hard drives have a life span with a median of roughly 6 years (extremetech.com). So you'll need to completely replace the entire array of drives no less than every 10 years.
- Some people will yell "Use SSD drives instead! No moving parts!" SSD (solid-state-disk) is a great thing and working without the physical moving parts of a traditional spinning disk hard drive it also has a lifespan (techreport.com). SSD currently costs a lot more than traditional spinning disk hard drives.
- A RAID uses a RAID controller. This controller maintains data parity over the array. It has a battery to keep the RAID from "crashing"during a power failure event. This battery must be monitored, conditioned and replaced as needed.
- You'll want a battery backup for this as well and the batteries will need to be replaced as needed.
- CD-R is supposedly good for 50-200 years. (otsa.com). I do not have faith in this however as I have had both CD-R and factory optical discs "rot" or physically degrade in much less times when stored in ideal conditions. I would keep a copy in a format like this but these tend to become irrelevant very quickly.
- The "Cloud" is a great idea but if you read the user agreements most of the vendors are in no way on the hook if your data gets destroyed (however unlikely). The "cloud" is still in its infancy and should never be the only means of backup.
