A particular picture copies by itself multiple times in camera roll every day
Porting this to a community wiki answer so it doesn't remain hanging, as I've seen similar questions asked a couple of times recently 

Some third-party messaging applications copy photos to the Camera Roll after receiving them, such as WhatsApp. Assuming you received it in a third-party application, there may be a bug in that application causing it to be saved repeatedly.

Try removing the photo from any 3rd party app it may have originated in.