Check out Amazon Glacier too - $0.011 / GB / month*. Around rupees 7 per month for 100 GB storage. Upto 1 GB per month download free. Since the topic being discussed is archival, upload and download won't be very frequent so transfer costs would be negligible. Check fastglacier.com for a windows client - free client should suffice for most purposes. Download has to be requested and might take around 4 hours for the download to be ready. Amazon has a solid business model behind the cheap storage so unlikely to fold up unlike photo-sharing websites which intend to sell ads to you so are tempted to look through your photos for context detection.
Above all, unlike privacy-less facebook / flickr / google photo services - you can encrypt the data before uploading and not share your photos with corporations , and governments by proxy.
*Ireland rates. US is cheaper but is likely to be laggier than Ireland, though mostly indistinguishable in practice.