The equivalent expression in many languages employs a preposition translated as “on” in most other contexts (e.g. “sur” in French). In English, however, the correct preposition is “in”:
The pattern is the same no matter what word we use for the visual media (e.g. image, photo, picture, drawing):
We only use “on” when we mean that something is on top of a physical object; for example “there’s a cup on a photo” means that the cup lies on a photo. However, “on” can also be used when one thing is part of the top layer of another thing. This can be a little confusing for words like “postcard”. You would say:
The reason is that a postcard is the piece of paper itself, not what’s printed on it (unlike the word “picture” which refers to the actual visual content). What you mean is in fact: “There’s a house (in a picture that is) on a postcard.” Similarly, if you saw a picture of a man drawn on an envelope, you wouldn’t say that there’s a man in an envelope, would you. The (picture of the) man is on the envelope.