If you are an avid user of Whatsapp, then you must have encountered one of those situations in which you get a picture and when you open it, the picture turns into something else.
For example- you get a picture. the thumbnail shows a pic of a girl, and when you tap on it, a picture of a bear appears instead.
I've found out that pictures like these are made using apps like FhumbApp(iOS) and MagiApp(Android).
Wasap Fake Image Trolling, this app also claims to do the same
How exactly does these apps conceal one picture inside another one?