Photo Forensics
Can You Tell If A Photo Has Been Retouched?
by Joelle Steele
Is it possible to determine if a photograph has been altered? This is a question I am often asked by private investigators, law enforcement officials, and attorneys who are trying to determine whether a photo has been edited — i.e., enhanced, retouched, manipulated, or “photoshopped” — with the intent to defraud or deceive. The answer is yes, usually, but not always.
Signs of Retouching
When alterations are made by a skilled photo editor, they know exactly how to avoid most tell-tale signs of retouching, how to cover their tracks. They can even skillfully alter hair color, a challenge at the very least. But with amateur photo editors — and there are far more of them — the changes are often quite blatant. Novice photo editors leave behind some of the obvious “tells” that a photo has been manipulated. These include inadvertently removing a shadow, leaving a shadow behind for an item they removed, or adding something to the photo and creating a shadow for it that goes in the wrong direction. Easy to detect if you know to look for it.
Other tells include intentionally blurring only certain signs or words to mask a location, but leaving other signs and words perfectly clear. Even if you look at these photos at the pixel level, you’re likely to find some very obvious signs that people have been removed from a photo (sometimes leaving a faint pixelated shadow), or that something was covered up using the clone stamp (rubber stamp). Such shoddy retouching is a dream come true when you’re trying to see whether or not a photo has been altered. In those cases, a good enlargement is usually sufficient to make that determination.
Flawless Alterations
It’s a different story when retouching is done by professionals. Trying to find even the slightest flaws in their work can be a daunting task. Notice I said “daunting,” not necessarily impossible, although it can be. In general, even professional photo editors can occasionally miss something in their efforts to manipulate an image. I have twice found instances where a shadow from a nose was facing the wrong direction and I have also found variations in eye reflections in several photos. I have even found variations in the light reflections on hair. These can all be hard to detect unless you are specifically looking for them.
Less obvious kinds of flaws in otherwise flawlessly altered photos are those of reflective surfaces. It is amazing how many times something or someone is immaculately removed digitally but is retained, in whole or in part, in a mirror or window pane. Lastly, there is careless cloning, using the clone stamp to replace something such as bricks in a wall by replicating the same brick over and over again.
Examining JPG Images
A common way to see if a photo has been altered is by looking at it in a program like Photoshop and examining the variations in the levels and curves. But that only indicates that the photo was edited, not necessarily what was done to it or where the changes were made to the image. It could be that the only changes were to contrast or color, not necessarily anything else. Most people look for those flaws in the pixels, but even that can provide unreliable results, especially if you are looking at a JPG image.
A JPG is a compressed file. More specifically, it is a “lossy” compression method, meaning that in order to reduce the file size, some of the digital information is discarded, resulting in a loss of image quality that is not evident at normal magnification. In fact, a fair amount of image data can be discarded before the degradation of the image is noticeable to the human eye. But, at the pixel level, the trained eye can see a combination of leftover compression “artifacts” consisting of grids, blurring, color changes, and jagged edges. When examining pixels, some people assume these things are the result of a photo being retouched, but they are actually the end product of the standard JPG compression process.
It takes a fair amount of experience to be able to detect the difference between compression artifacts and retouching when working with JPG images. Studying a TIF file (a non-compressed image file) and a JPG made from the same image is a good way to get a feeling for what JPG artifacts look like so that they will not be confused with the digital manipulations of a photo editor.
Summary
As you can see, it is not always a simple task to ascertain whether or not a photo has been altered. In the best case scenario, you’ll be looking at an amateur’s retouching and be able to see the obvious deficiencies in the resultant image. In the worst case scenario, you’ll be looking at the work of a professional photo editor and not be able to make such a quick determination. It takes time, patience, and practice to learn how to examine photographs and spot the signs of digital alterations.
This article last updated: 12/30/2014.
