Pictures gone after Nandroid backup restored Recently, I made a TWRP Recovery Nandroid backup of my current ROM, and I had just taken some personal pictures. In the backup, it included the /data partition. When I went to restore it, I opened the Photos app, and nothing was there. I checked the file system, and the camera and DCIM folders are empty. Is there any way to get the pictures back? 

I am on HTC One M8 GPe Android 5.1.
That is the way nandroid works. Its NOT some bug.

Yes, it does include /data partition but your data is stored in /data/media/0 which it skips during backup as this would lead it to backup everything inside internal memory increasing backup size significantly.

In other simple words, nandroid backup's /data option includes only apps and their data, not your personal data on internal or external sd.

As for restore, there are a bunch of apps that claim to be able to recover deleted/formatted data such as Undelete (you need to be Rooted for this one) but I have never personally tried one so can't say about the performance. So you will have to test those yourself.

Hope this helps.