The photo backup strategy differs from person to person. It all depends on the end use of photo files. It is not necessary that the one worked best for me will also prove the best for you. You can work out the best photo backup strategy that suits your needs and goal. Here is what my usual photo backup plan is. See if it meets your requirement too.
For instance, I copy all my photos directly on an external hard disk. So that this keeps the original backup of my photos. Then, I copy the ones that need to be edited on the main computer and edit them. Now I create a folder in the computer system that has all the important photos. Make copies of it on CDs, DVDs etc. A redundant backup is always good in my opinion as internal or external hard drive may fail anytime. Similarly, a small scratch on a CD or DVD can affect it badly. What I recommend is a mix of all these photo backup media along with an online photo backup.
So, the best photo backup strategy for me is a combination of External and internal hard drive + backup on CDs and DVDs and above all creating redundant backups of my photos on at-least two or more online photo services.
There are various online photo sharing websites you can upload your photos. I use multiple options to backup photos and be rest assured. Make sure you choose the best photo-sharing websites you can rely on. Few most popular photo sharing websites are; Google Photos, Flickr, SmugMug, SkyDrive / Onedrive, DropBox, Imageshack, Facebook etc.
So even if it’s not the ideal solution, backup your photos any way you can. The key is to keep testing the backup to make sure it’s working right! It could save you and others a lot of unnecessary grief.