Encrypt the files you want to upload with AES-256 or RSA-2048 and make sure you keep the private key stored somewhere as you'll require it for the decryption of the encrypted files. You can keep backups of the private keys in a text file stored on external removable disk devices (such as USB/external HDD), on your phone, or even write it down on paper if you have the time and patience (but make sure you wrote it down correctly if you do this, the key can be long sometimes and tricky to follow).
After encryption of the target documents (e.g. pictures) you want to make an archive (e.g. via
7-Zip) for all the documents and then you want to add the documents into the archive. Make sure the archive is password protected with at least AES-256 (
7-Zip supports this).
Then you want to upload the password-protected archive to a cloud host such as
Google Drive,
Mediafire,
Dropbox (maybe all of them if you want multiple backups hosted online). You won't need to necessarily worry about it being "safe" so much, but more so "reliable" for the hosting of the archive. The last thing you want is for them to revoke the upload/download unexpectedly, thus making it inaccessible... Of course, the host being secure is still important, however since the documents are all protected to a reasonable extent due to the previous steps, you won't need to worry about that as much.
If the cloud host becomes compromised by an attacker and a hacker obtains your archive containing your personal documents (or if the cloud hosts happen to access the files for whatever reason based on the privacy policy) they won't actually be able to use the documents. Firstly, the archive would be password protected (with at least AES-256 encryption) and the files within the archive would be protected, too. It would take them too much time to attempt to access the files (e.g. via brute-force of the password), thus making it a waste of time, especially since they may not be able to gain access after spending all the time on trying... And secondly, if anyone wanted some documents to use (e.g. someone else's photos) they can go online and get someone else's or find someone else's documents... it wouldn't be worth anyone's time spending the time and effort to brute-force the archive AND the encryption for the documents themselves afterwards.
Alternatively, you can just password-protect the archive or just encrypt the documents within the archive, but for increased security you should use both methods.
Make sure you use long passwords (at least 12 characters) which are more complicated (e.g. the archive password) - therefore make sure to include random usage of numbers and special characters. The longer and the more complex the password will increase the difficulty for brute-forcing of the password.
Just some suggestions!
Hope this helped, stay safe,
Wave.
