It is best not to rely on someone else to store your valuable photos. Cloud companies can go out of business. Cassette tapes used to be an ideal way to backup data, but they are magnetic and in some cases if your tape drive died and you did not have the same brand, sometimes another brand or model would not read your tape. Hard drives are mechanical. They can easily fail. CD/DVD's and possibly USB thumb drives are about the best alternatives right now. The publication "Care and Handling of CD's and DVD's - A Guide for Librarians and Archivists" explains storage very well. It is from NIST (500-252). It is too big (1.24 MB) to upload here ( 1 MB max). Store CD's or DVD's properly and they should last 50 years. The questions always are, will a player be available to read the media in 50 years, and will software be able to understand the compression of a jpg file or other file storage types. Most likely yes, but if it is an important family photo, it may be best to have it printed on quality paper at a good shop for long term use. As the publication says, the proper handling and storage of any media is most important. And use quality media, not Dollar Store closeouts if long term storage is needed.
If interested -
NIST Digital Media Group: digitalPhysicalMediaAndDevice
Scroll down to the Final pdf version - 50 pages (1.24 MB file)