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You may be asking yourself: "what if I can't recognize the difference between Good Photoshop and Bad Photoshop?" Chances are, if the first thing you think of when viewing an image is "Photoshop", something has given the game away. There's some element, some digital artifact, some telltale clue that the image has been altered. If you see repeating patterns, smeared or blurry regions where you'd expect some natural texture, or otherwise unnatural-looking features, you could be looking at Bad Photoshop. If you know the image has been altered for some other more abstract reason, such as an impossible scene, or "unlikely perfection", but the result is otherwise convincing and/or attractive, then it is not Bad Photoshop. That doesn't necessarily mean that it's good, however.
carefully observe the images below and use what you've learned to determine which is the Original, which is Bad Photoshop, and which is Good or at least Photoshop of Dubious Merit.