An easy way to tell: look at the edges of the text area's white background. See how they're kinda jaggy, almost like steps? That's due to low resolution. Either

An easy way to tell: look at the edges of the text area's white background. See how they're kinda jaggy, almost like steps? That's due to low resolution. Either the device is low res (which most smart phones are) or the source image was. Now look at the edges of the 3D watch's hands: they're all smooth at every angle. That means either a 3D mock-up or an incredibly high res screen. Yet look at the black watch face in the prior shot: all the hands are jagged.