It's called pareidolia. But here is the thing. Even you you believe you can see something, and even if you believe that editing an image to suggest something is effective (stories about people doing this verge on urban legends, there are never first person accounts, it's always hearsay), the evidence shows it doesn't work. Believing something doesn't make true.
It turns out the story that started the whole thing was a lie:
snopes.com: Popcorn Subliminal Advertising