Digital photography, Photoshop and synthetic computer graphics have made image trickery both easier to commit and harder to detect. But it is still possible to catch tamperingprovided you have a good eye and the right tools. Researchers at Dartmouth College have developed sophisticated algorithms for detecting manipulation of digital images in general and.jpegs in particular. The algorithms are still in the research laboratory, but you can download the algorithms and try them out yourself. There are also some clues unique to the digital world. For example, the vast majority of todays cameras take.jpeg-format digital pictures at sizes such as 640×480 or 1024×768.”]
Source: https://www.csoonline.com/article/2118840/how-to-tell-if-a-digital-image-has-been-altered.html