Why can't I delete some of the pictures from my photo library?

[iMore Question]

I have several pictures in my photo album on my iPhone 6 that I want to delete. However when I go to the picture, the trash can icon goes away. I took one of the pictures with my iPad and do not have iCloud sharing turn on. I don't even know how it got in my album.

 

[alexislgz]

Probably it was synced with itunes if that was the case the only way would be synching the phone back with itunes but choosing a photo folder with no photos