Disappearing photos in iPhone gallery

I have noticed that for the past 2 years some photos disappeared. But it usually happens with new photos. At first I was thinking that I have imagine it that I took a photo, but recently I was with a friend that also remembered that I took a photo, but when I checked the gallery there was no specific photo.

does anyone faced with similar problem?

[Re-Titled by Moderator]

Original Title: photos disappears