How to tell if an image has been digitally altered

Most of us have heard someone say something akin to “that photo has been photoshopped” when someone identifies what they think is an obviously fake image. While in the past digitally altered images might have been an easy-to-spot source of internet humour, they are now so hard to distinguish from reality that many people unwittingly pass on news based on entirely contrived images.

Luckily, forensic image experts have a few helpful tools and tricks in their arsenal that allows them to spot fake images rather quickly. While the everyday person won’t have the training or resources to pick out the most masterfully crafted fakes, there are some simple tricks they can follow to tell if the photos their friends have shared are real or not.

Let’s take a look at some of the easiest ways to tell if an image has been digitally altered.

Do a reverse image search

A reverse image search is an easy way to see if a certain image has been used elsewhere on the internet. This simple function can instantly tell you if a certain image has been altered by comparing it to almost identical images found elsewhere.

It can also tell you if a certain fake image has been used before. A good example is photos of sharks swimming down the streets during a flood whereby the same hoax image has been used across several similar events.

Examine light and shadows

While this method might seem like too much of an effort, it’s quite low-tech. Careful examination of how light and shadow appear in an image can tell you if something has been artificially inserted into it.

The most obvious of fakes will insert people or objects that don’t have shadows at all. Others will have shadows that are facing the wrong direction compared to the other people and objects in the scene.

Examine in editing software

When certain parts of an image are deleted they can leave behind some visual clues. Even things deleted and swashed over on a black background will leave a slight difference in colour density.

Simply playing with the contrast of an image can easily identify discoloured blocks where part of an image used to be. Those who have simply coloured over the blank spot with a background colour might fool the naked eye but not anyone who really looks for it.

Not all visual artefacts mean the image is fake

When images are compressed into formats such as JPEG they can lose some of their visual fidelity in the process. This means that the image has lost some visual information whilst being compressed.

This can lead people to wrongfully accuse an image of being altered because they have identified blocky artefacts in the picture. Be careful not to jump to conclusions about an image just because it has some signs of compression in it.