Photos mysteriously appeared in my phone album iPhone 4

I know what youre thinking, yeah right. But its true. I have three baby pictures that mysteriously appeared in my iphone 4 photo album the other day and Im trying to figure out how they got there. I didnt save them from messages or from the internet and no one had access to my phone. I noticed them last night when I was transfering pics to my computer (maybe something happened there...I dont know). If someone can explain, or had the same thing happen, please respond. My wife thinks I have another family somewhere. Cute kid, but not mine.
iphone 4 iOS 4