Can i recover data from a Nandroid Backup without the original device? I'd like to start making scheduled backups to my rooted OnePlus 3T (Oxygen OS 5.0.1) in order to prevent the loss of data from any reason that could occur.   

I want to save everything: the entire content of /sdcard and the apps+data. I know doing a Nandroid Backup with TWRP is the best way to make a complete backup of an Android device quickly, but i have a question:

Is it possible to recover data without the original device? If i had a totally new device, would it be possible to extract some specific data from the backup? (For example, read and extract the /sdcard/download directory from the backup, or also extract the data from a given app)
That would indeed be possible. There are several apps which are able to extract parts of a Nandroid backup, e.g. Titanium Backup or ROM Toolbox.

Apart from that, depending on the format used by your Nandroid backup, you can either mount them as loop device (disk images) or unpack them (tarballs) to invesigate/access all contents.

For further details, I'd recommend a look at our nandroid tag-wiki – and especially follow up to:


Restore only part of nandroid image
Extract App Data from Nandroid / CWM Backup